Table of Content

20 August 2022, Volume 31 Issue 8

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Drought risk status of grassland in China

Ying WANG, Jian-shun WANG, Qiang ZHANG

2022, 31(8):  1-12.  DOI: 10.11686/cyxb2021319

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Water deficit is the primary natural limitation restricting grassland productivity in China. Drought risk assessment is the core component of risk management. In this paper， by collecting meteorological， soil， vegetation， landform and other data， an assessment model for grassland drought risk in China was constructed after an in-depth analysis of this data. The model established an evaluation index system for drought risk， determined the weight of each index by the entropy weight method， and assessed the level of hazard， degree of exposure， sensitivity， and vulnerability. Based on a GIS spatial analysis function， an assessment and a regionalization analysis of grassland drought risk were then conducted for China. It was found that the high and sub-high drought-risk areas for grassland in China are mainly located in Inner Mongolia， the Hexi Corridor， the Qaidam and Tarim Basins， the western Qinghai-Tibetan Plateau and Yunnan. The high and sub-high drought exposure areas are mainly located in Southwest China and South China. The high and sub-high sensitive areas are mainly located in the southeast of Inner Mongolia， Northeast China， the South and east slopes of the Qinghai-Tibetan Plateau， the northern margin of Tarim Basin and the Southwest of China. The high and sub-high vulnerability areas are mainly distributed in the central and eastern parts of Inner Mongolia， the Hexi Corridor in Gansu， Northern Xinjiang， most of the Qinghai-Tibetan Plateau， Yunnan and eastern Sichuan. The high and sub-high risk areas for grassland drought are mainly located in the northeast of Inner Mongolia， the west of Northeast China， the North of Ningxia， the north edge of Tarim Basin， the South of the Qinghai-Tibetan Plateau， the Yunnan-Guizhou Plateau， Henan and Shandong. These results provide a theoretical framework and an initial scientifically-based evaluation for susceptibility to drought of grassland in China.

Estimation and digital mapping of grassland belowground biomass in the Altay region， China， based on machine learning

Fang-zhen LI, Hua-ping ZHONG, Ke-hui OUYANG, Xiao-min ZHAO, Yu-zhe LI

2022, 31(8):  13-23.  DOI: 10.11686/cyxb2021481

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This research investigated the spatial pattern of grassland belowground biomass （BGB） in the Altay region. Ecological indicators and BGB during the peak season （June-August） in 2015 were surveyed. Based on representative information for specific locations， terrain types， climate， and soil and plant factors， a forecasting model involving machine learning was developed to estimate BGB in the 0-30 cm soil layers in the study area. Based on this eatimation model， the spatial pattern was then obtained by the spatial interpolation method for digital mapping of BGB. It was found that： 1） The support vector machine model （SVM） had a higher estimation accuracy than an alternative partial least squares regression model and random forest model， also tested. The R² values from the SVM model for verification data were 0.77， 0.67 and 0.69， respectively in the 0-10 cm， 10-20 cm and 20-30 cm soil layers， with accompanying root mean square error （RMSE） values of 246.56， 98.81 and 63.58 g·m^-2， respectively. The outputs of three spatial interpolations indicated that an inverse distance weighting （IDW） method performed better than radial basis function and tension spline methods. 2） We further compared the output accuracy of different combinations of estimation model and spatial interpolation method. This comparison showed that SVM+IDW was a dependable combination of estimation model and spatial interpolation method for estimating the spatial pattern of BGB in the Altay region. The R² values of the digital map obtained from this combination in the 0-10 cm， 10-20 cm， and 20-30 cm soil layers were， respectively， 0.73， 0.64， and 0.60， and the RMSE values were 269.73， 108.14 and 73.01 g·m^-2. 3） The mean value of BGB in Altay region was 1265 g·m^-2， which was twice that of the average for China and comparable to the global mean value. Temperate meadow steppe had the largest BGB， with a mean value of 2908.50 g·m^-2， the temperate deserts hold the least biomass， estimated at 776.84 g·m^-2. The BGB in the whole region is 1.27×10⁸ t （≈0.13 Pg）. Our modelling identified a strong spatial variability that decreased from the north to the south and from the mountains to plains.

Relationship between cold resistance of alfalfa， degree of fall-dormancy and snow cover thickness in Northern Xinjiang

Jian-tao ZHAO, Ya-fei YUE, Qian-bing ZHANG, Chun-hui MA

2022, 31(8):  24-34.  DOI: 10.11686/cyxb2021299

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The climate in the north of Xinjiang Province is cold and extreme snowfall often occurs in winter that contributes to alfalfa cold injury and freezing injury with a decline in alfalfa stand production and consequent reduction in animal production potential. This study explored the variation in cold resistance， overwintering survival rate and hay yield of alfalfa （Medicago sativa） varieties with different fall-dormancy scores and with different snow-cover-thickness treatments in Northern Xinjiang. Alfalfa varieties tested were： AC Caribou （Dormancy score 1）， Concept （Dormancy score 3）， Magnum 551 （Dormancy score 5）， Sardi 7 （Dormancy score 7）， and WL656HQ （Dormancy score 9） and the experiment included snow cover thickness treatments of 0， 10， and 15 cm， achieved using plastic frames and addition or removal of snow to control snow depth on the experiment plots. Data collected included daily soil temperature in the root cap and in the surface layer （1-10 cm）， average water content in the surface layer （0-15 cm）， plant physiological indexes of cold resistance in the root and neck and overwintering survival rate of alfalfa plants. It was found that winter snow helped to maintain the temperature balance of the soil layer around the cap and neck of root of alfalfa， and the overwintering survival rates of alfalfa varieties with high fall dormancy were significantly increased under snow cover （P<0.05）. Compared with no snow covering， malondialdehyde content of alfalfa decreased， while soluble protein， water soluble carbohydrate content and hay yield increased with snow covering. Principal component analysis indicated that under 15 cm snow cover， Magnum 551 with fall-dormancy score 5 had excellent overall score for overwintering survival rate， cold resistance index and hay yield. Hence this variety is recommended as suitable for cultivation in northern Xinjiang.

Ten-year livestock exclusion did not affect water and nitrogen use efficiency of alpine desert-steppe plants in Northwest Tibet

Wei-ling NIU, Hui CHEN, Hui-xin HOU, Chen-rui GUO, Jiao-lin MA, Jian-shuang WU

2022, 31(8):  35-48.  DOI: 10.11686/cyxb2021289

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Under climate change and overgrazing， the area of degraded grassland is increasing in the Tibetan Autonomous Region of China. A common measure for recovering these degraded grasslands is grazing exclusion using fencing. However， the effects of fencing on plant functional traits and physiological processes are still unclear. In this study， we chose leaf carbon content （LCC） and leaf nitrogen content （LNC） and stable carbon and nitrogen isotopic compositions （δ¹³C and δ¹⁵N） to characterize the water use efficiency （WUE） and nitrogen use efficiency （NUE） of alpine desert-steppe plants in Northwest Tibet to clarify the effects of livestock exclusion by fencing on species WUE and NUE. We found that LCC， LNC， δ¹³C and δ¹⁵N of alpine desert-steppe plants differed between different plant functional groups. At both community and plant functional group levels， livestock exclusion had no significant effects on LCC， LNC， δ¹³C and δ¹⁵N. Rather， soil water content and pH value were the main factors affecting the community weighted mean of leaf δ¹³C， indicating that soil properties can significantly affect the internal WUE of plants. Growing season temperature was the dominant factor affecting the community weighted mean of leaf δ¹⁵N， indicating that climatic conditions are the main factor affecting ecosystem nitrogen cycle of alpine desert-steppes in Northwest Tibet. There were no trade-offs between WUE and NUE for alpine desert steppe plants. In conclusion， our study confirms that the short-term livestock exclusion in Northwest Tibet does not significantly alter the WUE and NUE of desert-steppe plants and that local environmental factors have significant effects on carbon and nitrogen cycling of the alpine desert-steppes. Therefore， it is necessary to study plant physiological and functional traits in response to environmental change for a better understanding of plant community assembly and evolution and to understand nutrient cycling in alpine grassland ecosystems.

Plant community composition and soil nutrient status of degraded alpine meadow sites in Northern Tibet

Yan PENG, Jing-yuan SUN, Su-jie MA, Xiang-tao WANG, Xue-hong WEI, Lei SUN

2022, 31(8):  49-60.  DOI: 10.11686/cyxb2020475

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This research investigated the community features， soil nutrient characteristics and their correlations in different degraded alpine meadows in Northern Tibet. Lightly degraded （LD）， moderately degraded （MD） and severely degraded （SD） alpine meadow sites were selected for study and our research used a combination of field investigation， laboratory measurement， variance analysis and redundancy analysis to elucidate the relationships between vegetation ecological characteristics and soil environmental factors for these three different alpine meadow degradation stages in Northern Tibet. It was found that： 1） There were 25 plant species from 20 genera and nine families present in the study area， and these were species with strong ecological adaptability， mainly from the in Cyperaceae， Poaceae， Asteraceae and Rosaceae families. Species associations commonly present across these alpine meadow sites included Kobresia pygmaea with Pedicularis longiflora， Leontopodium pusillum with K. pygmaea and Potentilla bifurca with Ajuga lupulina. Among these， K. pygmaea was the dominant species at LD and MD sites， although the functional groups were dominated by forbs. The perennial herb is the major vegetation component in Northern Tibet. 2） The characteristics of the studied plant communities， including aboveground biomass， height， density， frequency and vegetation cover showed a decreasing trend from LD to SD （P<0.05）. And the species Margalef index， Pielou index， Simpson index and Shannon-Wiener index of the LD sites had the highest values. 3） With increasing alpine meadow degradation， organic matter， total nitrogen， total phosphorus， total potassium， available nitrogen， available phosphorus and available potassium all decreased， while pH increased. 4） Species diversity index and the available phosphorus and total phosphorus across the series of degradation stages were significantly positively correlated. The aboveground biomass showed significantly positive correlations with total nitrogen. The factors contributing most strongly to vegetation growth in these alpine meadows at different stages of degradation were available nitrogen， organic matter and pH， respectively. This indicated a correlation between the degradation status of alpine meadows， plant community composition and soil nutrient status. In summary， the soil nutrient status， especially the role of soil nitrogen and phosphorus， must be considered when researching and managing alpine meadow degradation．

Effects of clipping by plateau pika on plant interspecific associations in alpine meadows in the Qinghai Lake Region

Hao-hao QI, Xiao-pan PANG, Su ZHOU, Zheng-gang GUO

2022, 31(8):  61-71.  DOI: 10.11686/cyxb2021306

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Plateau pikas prefer to clip the tall plants in thick alpine meadow， which often alter the interspecific and intraspecific relationships among plants in the meadow. This study used the variance ratio， Chi-square （χ²） test and Spearman rank correlation coefficient to determine the effects of clipping by plateau pikas on interspecific association among plants. It was found that the clipping by plateau pikas resulted in the overall interspecific association being transformed from a non-significant positive association to a significant negative association， and decreased the stability of the plant community. The clipping by plateau pikas decreased the number of paired species with positive interspecific association and positive correlation， while it increased the number of paired species with negative interspecific association， no-interspecific association and negative correlation. The overall results of χ² testing， association coefficient （AC） value and Ochiai （OI） index showed that there were no significant interspecific associations among most species pairs in the plant community， and the interspecific associations were unstable. These results indicate that the χ² test and Spearman rank correlation coefficient can be used to quantify the effect of small herbivores on plant interspecific associations， and provide basic information on the responses of plant community structure to disturbance by plateau pika.

Plant cluster structure and leaf functional characters of Agropyron mongolicum populations in different plant species associations

Wan-long LIU, Dong-mei XU, Jia-mei SHI, Ai-yun XU

2022, 31(8):  72-80.  DOI: 10.11686/cyxb2021293

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This study explored the changes in population dynamics and leaf morphological traits of Agropyron mongolicum across three different plant community associations： A. mongolicum+Astragalus melilotoides （MC）， A. mongolicum+Cynanchum komarovii （ML） and A. mongolicum+Lespedeza potaninii （MN） in desert steppe in Yanchi County， Ningxia. The individual plants of A. mongolicum were classified according to their basal diameter into grade I plant clumps （0-2.0 cm）， grade Ⅱ plant clumps （2.1-4.0 cm）， grade Ⅲ plant clumps （4.1-6.0 cm）， grade Ⅳ plant clumps （6.1-8.0 cm）， grade V plant clumps （8.1-10.0 cm） and grade Ⅵ plant clumps （>10.0 cm diameter）. The plant clump size and leaf functional traits of A. mongolicum and their relationships with habitat factors were studied. It was found that in the MC and MN communities of A. mongolicum， there were more A. mongolicum plant clumps of grade I and grade Ⅱ， while in the ML community， the population density of A. mongolicum was lower， with grade Ⅲ and grade Ⅳ plant clumps being dominant. The leaf area and specific leaf area of A. mongolicum in the MC and ML communities of A. mongolicum were， respectively， 4.68 cm² and 41.2 cm²·g^-1， 4.70 cm² and 39.2 cm²·g^-1， which was significantly higher than values of 3.38 cm² and 27.7 cm²·g^-1 recorded in the MN community of A. mongolicum. The clump size of A. mongolicum was correlated with total potassium， while the soil moisture， organic carbon， total nitrogen and total phosphorus were the main factors affecting the leaf functional traits of A. mongolicum. Therefore， A. mongolicum exhibited adaptation to habitat changes in different species associations by altering its population distribution and leaf morphological traits.

Responses of photosynthetic characteristics of Leymus chinensis in temperate typical steppe to component factors of simulated grazing

Ze-dong ZHOU, Hui-ling MA, Xu HAN, Yuan-heng LI, Xi-liang LI, Kun-na LI

2022, 31(8):  81-89.  DOI: 10.11686/cyxb2021267

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Grazing is a compound stress， including factors such as feeding， trampling， and dung and urine return. In order to clarify the separate impacts on grassland of the components of grazing， this study simulated the process of livestock grazing by mowing， artificial simulated trampling， and artificial manure addition. Using Leymus chinensis as a model plant， the responses of plant height， vegetation cover， dry weight and photosynthetic characteristics of L. chinensis leaves to components of the grazing process were studied. It was found that feeding and treatments containing feeding factors significantly reduced the cover， height and dry weight of L. chinensis， but increased the net photosynthetic rate， transpiration rate， stomatal conductance， and intercellular CO₂ concentration， but reduced the water use efficiency of L. chinensis leaves. L. chinensis plant height was significantly negatively correlated with net photosynthetic rate， stomatal conductance， intercellular CO₂ concentration， and transpiration rate， and significantly positively correlated with water use efficiency. Soil water content， stomatal conductance， intercellular CO₂ concentration and transpiration rate were significantly positively correlated. Relatively speaking， trampling and feces and their interaction have a weaker effect on L. chinensis than herbage consumption. Overall， defoliation through livestock feeding is the main factor affecting the photosynthetic characteristics of L. chinensis in temperate typical steppe.

Physiological response of Viola tricolor to NaCl stress

Shi-ping SU, Xiao-e LIU, Jie XI

2022, 31(8):  90-98.  DOI: 10.11686/cyxb2022026

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This research investigated the physiological response mechanisms and growth characteristics of Viola tricolor in response to NaCl stress and explored the maximum NaCl concentration tolerated by V. tricolor. In a pot experiment， 45-day old seedlings of V. tricolor were subjected to different NaCl concentrations （0， 25， 50， 100， 150 and 200 mmol·L^-1）. It was found that NaCl treatment at higher concentrations had obvious effects on the osmotic regulation system， antioxidant enzyme system， photosynthetic pigment， malondialdehyde content and plant height of V. tricolor. With increase in NaCl concentration， soluble sugar， soluble protein， free proline and chlorophyll contents， together with catalase， peroxidase and superoxide dismutase activities， initially increased and then decreased. MDA concentration exhibited a pattern of continuous increased， and height growth decreased on the 14th day of NaCl stress with increasing NaCl concentration. A membership function analysis showed no obvious inhibitory effect of NaCl on the growth of V. tricolor when the concentration of NaCl in soil was ≤150 mmol·L^-1 but in contrast， NaCl had an obvious inhibitory effect on V. tricolor growth when the concentration was >150 mmol·L^-1. Therefore， the maximum NaCl concentration tolerance of V. tricolor was 150 mmol·L^-1， above which， the metabolic regulation system and antioxidant enzyme system were seriously affected， chlorophyll degradation was intensified， the photosynthetic system was seriously damaged， and the growth of V. tricolor was seriously reduced.

Comparison of nutritional value of oat hay， oat silage and Sichuan pasture for yaks

Yin-jie YOU, Hao-zhen ZHOU, Yao LIU, Chen-xi WANG, Zhong-li PENG

2022, 31(8):  99-110.  DOI: 10.11686/cyxb2021432

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This experiment compared the nutritional value of forages conventionally fed to yaks in Sichuan. Oat （Avena sativa） hay， oat silage and Sichuan pasture were analyzed for their nutritional value and in vitro gas production. An in vivo digestion experiment was conducted in Hongyuan， Sichuan Province. Maiwa male yaks （n=9） with an initial body weight of 150±10 kg were randomly divided into 3 treatment groups with 3 yaks in each group. It was found that： 1） The crude protein （CP） content of pasture was significantly higher than that in oat silage and oat hay （P<0.05）. The neutral detergent fiber （NDF） and acid detergent fiber （ADF） content of pasture was significantly lower than that in oat silage （P<0.05）. 2） The non-protein nitrogen content in oat silage was significantly higher than that in oat hay and pasture （P<0.05）. The rapidly degraded protein， moderately degraded protein and slowly degraded protein contents in pasture were the highest and the unavailable protein content was the lowest. The unavailable fiber content in oat silage was significantly higher than that in pasture and oat hay （P<0.05）， while the slowly degraded fiber and non-structural carbohydrate contents were significantly lower than those in pasture and oat hay （P<0.05）. 3） The NDF and CP digestibility of pasture were significantly higher than those of oat hay and oat silage （P<0.05）. The ADF digestibility of pasture was significantly higher than that of oat silage （P<0.05）， but did not differ significantly from that of oat hay （P>0.05）. 4） The NH₃-N concentration in the rumen fluid of yaks in the pasture treatment group was significantly higher than in animals fed oat silage and oat hay （P<0.05）， and the micro crude protein yield was significantly higher in the pasture diet than that in the oat hay diet but did not differ significantly from that in the oat silage diet. Oat hay had the highest total volatile fatty acid yield. 5） The gas production of animals fed pasture was significantly higher than that of animals fed oat silage （P<0.05）. Overall， rumen fermentation results reflected the predictions from diet component analysis using the cornell net carbohydrate and protein system （CNCPS） and in vitro gas production results were basically consistent with the results of nutrient digestibility and rumen metabolites determined by the yak in vivo digestion test. These results indicate that it is feasible to evaluate the nutritional value of yak roughage using the CNCPS and in vitro gas production methods. The nutritional values of the three forages were： pasture>oat hay>oat silage.

Agronomic traits and fermentation quality of maize silage harvested at different grain-development stages in irrigated drought areas of southern Xinjiang

Dong-qing FU, Chun-ying JIA, Li ZHANG, Fan-fan ZHANG, Chun-hui MA

2022, 31(8):  111-125.  DOI: 10.11686/cyxb2021273

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To study the changes in agronomic traits and fermentation quality of maize silage harvested at different stages of grain development in desert irrigated areas and to screen for the best-performing maize silage cultivars in the Third Division area， four silage-specific and 11 grain-feeding maize varieties were evaluated， and agronomic traits determined. Silages were prepared at the grain-filling stage， and when the milk line reached the 3/4 milk stage， 1/2 milk stage and 1/4 milk stage， of grain development. Nutrient composition， fermentation quality and in vitro digestion were measured after 60 days of fermentation， and the agronomic traits， nutrient composition， fermentation quality and digestion characteristics were used as evaluation indexes for the multi-factor evaluation of the 15 maize varieties using the similarity priority ratio method. It was found that silage corn plant height， cob position， fresh dry herbage yield， whole plant fresh weight， stalk fresh weight， cob fresh weight， seed fresh weight， dry matter （DM）， crude protein （CP）， water soluble carbohydrates （WSC）， starch content and metabolizable energy increased incrementally as grain development progressed， and reached a peak at the 3/4 milk stage. Among the varieties， Dafeng 30 had the highest fresh herbage yield， Jinyu 9 had the highest DM content， Xinsiyu No. 10 had the highest CP content， Xianyu 696 had the highest WSC content， and Tunyu 765 had the highest starch content， with values significantly different from other varieties （P<0.05）. Conversely， the contents of neutral detergent fiber （NDF）， acid detergent fiber （ADF）， the ratio of ammonia nitrogen：total nitrogen （NH₃-N∶TN）， the organic matter digestibility （OMD） and the gas production rate decreased incrementally as the reproductive period progressed， and ADF， NDF and NH₃-N/TN were lowest at the 3/4 milk line stage. Among the varieties， ADF content was the lowest in Xinsiyu No.12， NDF content was the lowest in Xinsiyu No.10 and NH₃-N∶TN was the lowest in Xinsiyu No.11 at the 3/4 milk line stage， with their values significantly different from other varieties （P<0.05）. OMD and gas production rate peaked in the filling period， with Xianyu 696 having the highest OMD and Xinsiyu No. 10 having the highest gas production rate， with both significantly different from other varieties （P<0.05）. The pH of the silage of each maize variety initially decreased and then increased at different grain-development stages， while the lactic acid （LA） content initially increased and then decreased， and there was no significant pattern of change with fertilizer in acetic acid and propionic acid. The silage pH value was lowest when harvested at the 1/2 milk line stage， and the variety with lowest pH was Tunyu 765. Silage LA content was highest when harvested at 1/4 milk line stage， with Xinsiyu No.12 significantly higher than from other varieties （P<0.05）. In summary， harvest of silage maize at the 3/4 milk line stage produced high yielding and high quality silage forage， and the multi-factor scores of Xinwo No.1， Tunyu 765 and Dafeng 30 were highest among the tested varieties. Therefore these three varieties are recommended for planting in the Third Division area of Xinjiang and in ecologically similar regions.

Effects of planting density and nitrogen application on leaf enzyme activity and water-nitrogen utilization of silage maize under ridge furrow rainwater harvesting in Loess Plateau

Da-liang ZHOU, Wei SHI, Zi-wei JIANG, Zheng-ye WEI, Huan-huan LIANG, Qian-min JIA

2022, 31(8):  126-143.  DOI: 10.11686/cyxb2021315

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A field experiment was conducted in Huan County， Gansu Province， to explore the effects of planting density and nitrogen application levels on leaf enzyme activity and water-nitrogen use efficiency of silage maize （Zea mays） under ridge furrow rainwater harvesting. Four planting densities （D₁： 6×10⁴ plants·ha^-1； D₂： 7.5×10⁴ plants·ha^-1； D₃： 9.0×10⁴ plants·ha^-1； D₄： 10.5×10⁴ plants·ha^-1） and four nitrogen application levels （N₀： 0 kg·ha^-1； N₁： 120 kg·ha^-1； N₂： 240 kg·ha^-1； N₃： 360 kg·ha^-1） were included in the experiment. In summary， it was found： 1） The activities of nitrate reductase （NR）， superoxide dismutase （SOD） and catalase （CAT） decreased with increase in plant density. However， the NR， SOD and CAT activity increased with N application and at the grain filling stage were significantly higher under N₂ and N₃ treatments than in the N₀ treatment. 2） The fresh and hay yield increased incrementally with increase in plant density. The average fresh and hay yield of the N₃ treatment was numerically highest， but the difference between N₃ and N₂ treatments was not statistically significant. 3） The precipitation utilization efficiency （PUE） and biomass water use efficiency （WUE_B） of D₃ and D₄ treatments were significantly higher than those of D₁ and D₂ treatments， and the grain yield water use efficiency （WUE_G） of D₃ treatment was greater compared to other treatments. Moreover， PUE， WUE_B and WUE_G of N₂ and N₃ treatments were significantly higher than those of N₀ and N₁ treatments. 4） The nitrogen content of D₃ and D₄ treatments was less than that of D₁ treatment， but the nitrogen uptake， nitrogen agronomic efficiency （AEN） and nitrogen use efficiency （NUE） of D₃ and D₄ treatment were significantly higher than those of treatment D₁. With increase in nitrogen application rate， nitrogen content and nitrogen uptake increased， while AEN and NUE initially increased and then decreased as nitrogen application rate increased. There was no significant interaction between planting density and nitrogen application rate for leaf enzyme and water-nitrogen use efficiency in our experiment. Among all the treatments， NUE， WUE_G and WUE_B were the highest in D₃-N₂ treatment， and higher yield was obtained. These results indicate that D₃-N₂ is a suitable agronomic management regime for silage maize production in the Loess Plateau.

A comparative study of silage quality characteristics of whole-plant， whole-ear and whole-straw silage of different maize varieties （lines）

Ying-zheng LI, Yu-lin CHENG, Lu-lu XU, Wan-song LI, Xu YAN, Xiao-feng LI, Ru-yu HE, Yang ZHOU, Jun-jun ZHENG, Xing-yu WANG, De-long ZHANG, Ming-jun CHENG, Yun-hong XIA, Jian-mei HE, Qi-lin TANG

2022, 31(8):  144-156.  DOI: 10.11686/cyxb2021479

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This study investigated the whole-plant， whole-ear and whole-straw silage efficiency and utilization characteristics of different maize lines. Three new strains of dual-purpose grain and fodder maize （MTP-044， MTP-080 and MTP-082； bred by Sichuan Agricultural University Maize Research Institute） and one silage maize strain （Yayu No. 8； Sichuan Yayu Technology Co. Ltd.） were studied. Biological yield and related agronomic characters were measured at the three-fourths milk line grain development stage， and samples ensiled. Under this criterion the time from planting to harvest of the four varieties or lines was 120 to 123 days. The nutritional value and fermentation quality of whole-plant， whole-ear and whole-straw silages were measured after 60 days of fermentation. The growth stage at harvest， the number of green leaves and the ratio of green leaves were the highest in MTP-080. The fresh and dry yields of whole-plant silage and whole-ear silage of MTP-082 were the highest. Whole plant silage of Yayu No.8 had the highest neutral and acid detergent fiber contents， and MTP-082 had the highest crude protein， starch and water soluble carbohydrate contents. The net energy for lactation of MTP-082 was significantly higher than that of Yayu No.8 and MTP-080. In addition， the pH of the whole-plant and whole-ear silages of each variety or line ranged from 3.53-4.07， the ammonia nitrogen/total nitrogen was less than 10%， and the flieg score was above 110 in each variety or line. The overall evaluation of the silage fermentation quality was excellent. The total energy， total digestible nutrients， digestible energy， metabolizable energy， net maintenance energy， net energy for gain and net energy for lactation of whole-ear silage were significantly higher than those of whole-plant silage and whole-straw silage. The relative feeding value of whole-ear silage was 2.05 and 3.37 times that of whole-plant silage and whole-stalk silage， respectively. In general， the dual-purpose grain and forage maize varieties such as MTP-082 exhibited high yield， desirable stay-green characteristics， excellent nutritional value and fermentation quality when used for whole-plant silage， and also provided high-quality raw material for whole-ear silage. The development of whole-ear silage made from dual-purpose grain and fodder silage maize adjusting ensiling measures to local conditions will help the maize planting and breeding industry to save costs and increase efficiency.

Effects of lactic acid bacteria and calcium propionate on fermentation quality and mycotoxin contents of whole plant maize and oat silages

Ji-peng TIAN, Bei-yi LIU, Hong-ru GU, Cheng-long DING, Yun-hui CHENG, Zhu YU

2022, 31(8):  157-166.  DOI: 10.11686/cyxb2021326

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This study evaluated the effects of compound lactic acid bacteria inoculants and calcium propionate on the fermentation quality， chemical composition， microbial counts， mycotoxin contents and aerobic stability of whole plant maize and oat silages. The two forages， whole plant maize and oats， were ensiled for 120 days in an experiment with four treatments： a control treatment （CK）， addition of compound lactic acid bacteria （LAB treatment）， addition of calcium propionate （PACA treatment） and addition of a combination of LAB and PACA. The application rates of LAB and PACA group were separately 5×10⁵ CFU·g^-1 and 0.4% of the fresh material. It was found that the fermentation quality of maize silages was very good while for oat silages the butyric acid and ammonia nitrogen contents were very high after storage. The effects of the additives on the silage quality of whole plant corn and oat silages were varied. All additives significantly increased the lactic acid and acetic acid contents and decreased the pH value， butyric acid， ammoniac nitrogen contents and yeast counts of oat silages （P<0.05）. While the PACA and LAB+PACA treatments showed better aerobic stability， significantly increased starch and soluble carbohydrate contents and decreased the mould and yeast counts of the whole plant maize silage （P<0.05）. The aflatoxin B1 content was reduced by the LAB and LAB+PACA treatments only in the maize silage （P<0.05）. The propionic acid content was only increased by the PACA and LAB+PACA treatments， but this effect was seen in both the whole plant maize and oat silages. Therefore， the combination of LAB and PACA treatments provides an important improvement in silage quality for whole plant maize and oat silages.

Effects of enzyme additives on fermentation quality and in vitro digestion characteristics of rice straw silage

Yong-jie WU, Hao DING, Tao SHAO, Jie ZHAO, Dong DONG, Tong-tong DAI, Xue-jing YIN, Cheng ZONG, Jun-feng LI

2022, 31(8):  167-177.  DOI: 10.11686/cyxb2021312

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This research investigated the effects of cellulase， xylanase and their combination on the structural and water-soluble carbohydrate components， in vitro digestion characteristics and fermentation quality of rice straw silage. Four treatments were set up as follows： 1） 0.3% distilled water， control （CO）； 2） 0.3% cellulase （CE）； 3） 0.3% xylanase （XE）； 4） a mixture of 0.15% cellulase and 0.15% xylanase， combined enzyme group （CX）. Samples were taken and analyzed after 3， 7， 14 and 30 days of ensiling. Compared to the CO treatment， CE， XE and CX treatments had significantly （P<0.05） higher lactic acid， glucose， fructose and sucrose contents， but significantly （P<0.05） lower pH values， ammonia nitrogen， total volatile fatty acid， acid detergent fiber， neutral detergent fiber， cellulose and hemicellulose contents and dry matter loss. The enzyme additives significantly （P<0.05） increased the cumulative gas production at 24， 48 and 72 hours and in vitro dry matter digestibility of rice straw silage. The CX treatment had the highest （P<0.05） lactic acid content （34.13 g·kg^-1 DM）， in vitro gas production （68.27 mL）， in vitro dry matter digestibility （61.31%） and the lowest pH value （4.36） at the end of ensiling. In addition， the CX group had numerically （P>0.05） or significantly （P<0.05） higher glucose， fructose and sucrose contents than CE and XE groups during ensiling. In summary， the addition of enzymes promoted the degradation of structural carbohydrates， increased the water-soluble carbohydrate content， and improved the fermentation quality and in vitro digestibility of rice straw silage. The CX treatment performed better than the CE and XE treatments， as indicated by superior fermentation quality， higher carbohydrate degradation and conversion， and better in vitro digestion characteristics.

Screening， identification and characteristics of low-temperature-tolerant plant growth promoting rhizobacteria in alpine meadow

Xiao-ting LIU, Tuo YAO

2022, 31(8):  178-187.  DOI: 10.11686/cyxb2021311

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The study aimed to isolate and screen low-temperature-tolerant plant growth promoting rhizobacteria （PGPR） from the rhizosphere of the dominant plant species in alpine meadows， with a view to using the PGPRs in restoration of grassland degradation. Nitrogen-fixing， phosphorus-dissolving and phytohormone secreting bacterial species were screened by selective media and subsequently the superior strains were identified by 16S rRNA molecular biology techniques. The results indicated large numbers of bacteria in the rhizosphere of Festuca kirilowii， Koeleria cristata and Roegneria purpurascens. The quantitative distribution of bacteria exhibited a strong rhizosphere effect， with bacteria numbers on the rhizoplane or surface of roots （RP）>on soil adhering to roots （RS）>histoplane or interior of roots （HP）. In total， we obtained 76 strains of PGPR， of which 30 were nitrogen-fixing bacteria with their nitrogenase activity ranging between 124.61 and 311.04 nmol C₂H₄·h^-1·mL^-1. A further 24 strains were active in dissolution of inorganic phosphorus （249.85-558.07 μg·mL^-1 in test solution）， while 22 strains could dissolve organic phosphorus 52.25-158.77 μg·mL^-1 in test solution）. Of the strains of PGPR with high nitrogenase activity or phosphate-solubilizing ability 27 strains were further selected for determination of plant hormone secretion. Results indicated that 26 strains of PGPR secreted GA₃， with the secretion amounts ranging from 0.60 to 52.91 μg·mL^-1 of test solution. Meanwhile， 18 strains of PGPR secreted IAA with the levels in test solution ranging from 0.11-1.53 μg·mL^-1， and all strains secreted t-Z at less than 0.31 μg·mL^-1. Preliminary identification of 14 superior PGPR strains using phylogenetic analysis determined that these belong to the bacterial genera Pseudomonas， Acinetobacter， Pseudarthrobacter and Variovorax. The superior PGPR strains detected in this study are potentially valuable bacterial resources that could be used for the development of microbial fertilizers suitable for vegetation restoration in alpine regions.

Analysis of drought and salt resistance of EeHKT1；4 gene from Elytrigia elongata in Arabidopsis

Yong ZHANG, Xiao-xia TIAN, Ming-li ZHENG, Pei-chun MAO, Lin MENG

2022, 31(8):  188-198.  DOI: 10.11686/cyxb2021304

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Plant high-affinity potassium transporter （HKT） genes encode K⁺ or Na⁺ transport or K⁺-Na⁺ co-transport plasma membrane channel proteins， which play an important role in the process of plant stress resistance. This research investigated the function of EeHKT1；4 in Elytrigia elongata （GenBank： KF956112.1）. An EeHKT1；4 overexpression plant expression vector was constructed and transformed into Arabidopsis thaliana， and the drought and salt tolerance of transgenic Arabidopsis plants were evaluated and analyzed. No difference was found in the primary root length between wild-type （WT） and transgenic lines under normal growth conditions， but NaCl and mannitol treatments inhibited the growth of WT and transgenic plant roots， and inhibited the root length of transgenic lines more than the root length of WT under the same drought and salt treatment conditions. There was no significant difference between WT and transgenic lines under normal growth conditions， but under NaCl and mannitol treatment， WT showed leaf atrophy and yellowing， while only some plants in transgenic lines showed leaf atrophy， and the survival rate of transgenic lines was higher than WT under the same stress conditions. Nitroblue tetrazolium and diaminobenzidine staining results showed that the leaf staining in WT and transgenic lines was relatively weak under normal growth conditions， and the intensity of staining in all leaves gradually deepened with increase in NaCl and mannitol concentration. Also， the intensity of staining in the WT was higher than transgenic lines under the same stress. With the expression level under normal growth conditions as the control， AtSOS1 gene were incrementally up-regulated in WT and transgenic plants with increase in NaCl concentration， and the expression levels in the transgenic plants were higher than that in WT. The expression of the gene AtNHX1 was up-regulated under NaCl treatment and the expression level in transgenic plants was lower than in the WT. Except for a transgenic line ‘L5’， no change in AtNHX1 gene expression associated with increase in NaCl concentration was detected in WT or transgenic lines. The genes AtRD29B and AtP5CS1 were both up-regulated under mannitol treatment， and their expression levels in transgenic plants were higher than in WT plants. In summary， EeHKT1；4 overexpression reduced the accumulation of superoxide anion and H₂O₂ in A. thaliana under adversity stress， induced the up-regulated expression of stress-resistant genes， and enhanced the drought and salt tolerance of A. thaliana.

Development of SSR markers based on full-length transcriptome sequencing and genetic diversity analysis of Halogeton glomeratus

Lu-juan SUN, Jian-jun HE, Jun-cheng WANG, Li-rong YAO, Er-jing SI, Ke YANG, Bao-chun LI, Xiao-le MA, Xun-wu SHANG, Ya-xiong MENG, Hua-jun WANG

2022, 31(8):  199-210.  DOI: 10.11686/cyxb2021234

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In this study， we used MISA online software to search for SSR loci at the transcriptome level of Halogeton glomeratus based on the full-length transcriptome data of H. glomeratus. A total of 29640 SSR loci were identified. The frequency of each SSR locus was 4.93 kb. SSR types included one- to six-nucleotide repeats， with the number of repeats ranging from four to 20， of which the trinucleotide repeats were the highest， at 38.25% of the total. Tetranucleotide repeats were the least common， comprising only 3.26%. A total of 327 SSR repeat types were identified， the frequencies of A/T， AG/CT， ATC/GAT and AAG/CTT repeat types were much higher than others. Further， SSR markers were developed and the genetic diversity of H. glomeratus from 18 different ecological sites in Gansu was analyzed. From the available 29640 SSR markers， 218 pairs of markers were identified as candidates for polymorphism screening， and 33 pairs of markers with high polymorphism were screened. A total of 199 alleles were detected for these markers， with the number of alleles varying from three to 13 and an average of 6.03. The gene diversity index （GD） ranged from 0.583 to 0.869 with an average of 0.698； the number of genotypes （GN） ranged from two to 13 with an average of 5.88； the polymorphism information content value varied from 0.527 to 0.856 with an average of 0.623. Cluster analysis indicated that the genetic similarity coefficient （GS） of H. glomeratus ranged from 0.528 to 0.859 with an average of 0.683 for 18 different ecological sites in Gansu. At a GS of 0.68， the tested materials were divided into four categories. This study provides reference data for the development and utilization of H. glomeratus germplasm resources.

Research progress on regulation mechanism of rhizome development in herbaceous plants of the Poaceae

Jia-lin LI, Sheng-lin JIANG, Yun-xia LI, Xiao-yan QUAN, Wen-bo WANG, Qiu-li SHAN, Chun-juan XIE, Ning YIN, Yu-xiang QIN, Li-hua ZHANG, Hong-mei LI, Wen-xing HE

2022, 31(8):  211-220.  DOI: 10.11686/cyxb2021274

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Rhizomes are creeping underground stems that serve as vegetative organs for clonal growth of perennial grasses and other monocots. The continuous differentiation and lateral extension of rhizomes endow rhizomatous grasses with strong abilities of horizontal expansion， migration and resistance to disturbance， which play important roles in both the formation of natural grassland species associations and the improvement of fragile ecosystems such as degraded grasslands， deserts， sand dunes. The differentiation and development of rhizomes is a complicated process co-regulated by internal factors and external stimuli. In this review， the recent research literature on the rhizomatous growth and development of grasses was systematically summarized. The regulation and response factors of rhizomatous growth and development were identified from the perspectives of habitat heterogeneity， plant hormone factors and related genes. This provides a theoretical framework for further research on the development of rhizomes and thus guides thinking on spatial expansion of rhizomatous grasses and the logic of ecological adaptation.