Drought tolerance of wild Elymus nutans during germination and seedling establishment

doi:10.11686/cyxb2020396

Abstract

Abstract:

Elymus nutans is a suitable forage grass for growing in the cold and semi-arid environment in the Three-River Headwaters region. In this study， we evaluated the drought tolerance and water demand threshold values of E. nutans during the germination and seedling establishment stages. For these analyses， seeds were germinated on paper under drought conditions simulated using the polymer polyethylene glycol （PEG-6000）. Solutions of PEG-6000 （-0.15， -0.30， -0.50， -0.75 and -1.00 MPa） were prepared to impose different levels of drought stress， with ultrapure water （0 MPa solution） as the control. The main findings were as follows： drought stress reduced the seed germination emergence percentage and germination emergence rate of E. nutans， delayed the peak period of seed germination and seedling emergence， and also delayed the peak period of seed germination and seedling emergence after re-watering. The seed germination percentage， seedling emergence percentage， germination index， vigor index， bud length， dry and fresh weight of buds， and dry matter accumulation of E. nutans decreased with increasing severity of drought stress. The root length and dry and fresh weight first increased and then decreased with increasing severity of drought stress. After re-watering， the seed germination percentage， seedling emergence percentage， germination index， and vigor index of E. nutans first increased and then decreased with increasing severity of drought stress， while the root length， bud length， and dry and fresh weight of root and buds decreased. Drought stress had little effect on the root elongation of E. nutans， but strongly affected bud elongation， and this effect became stronger with increasing severity of drought stress. Consequently， the root to shoot ratio of seedlings increased continuously with increasing severity of drought stress. The water demand threshold values of E. nutans varied during the period of germination and seedling emergence stages showed different requirements on environmental water potential. The germination stage had strong drought tolerance. Re-watering after drought stress positively affected seed germination and seedling emergence. Even under severe drought stress （-0.50 MPa）， seeds could still germinate and grow after re-watering. The results of this study have important theoretical value for further research on the drought adaptation mechanism of E. nutans， and also have practical significance for growing E.nutans to effectively control grassland degradation， desertification， soil erosion， and water loss in the Three-River Headwaters region.

Key words: Elymus nutans, germination and seedling emergence, water deficit, re-watering, water demand threshold value, Three-River Headwaters Region

Chuan-qi WANG, Wen-hui LIU, Yong-chao ZHANG, Qing-ping ZHOU. Drought tolerance of wild Elymus nutans during germination and seedling establishment[J]. Acta Prataculturae Sinica, 2021, 30(9): 76-85.

Figures/Tables 12

Fig.1 Effects of drought stress and rewatering on seed germination process

Fig.2 Effects of drought stress and rewatering on seed emergence process

Table 1 Effects of drought stress on seed germination and emergence

指标 Index	环境水势Environmental water potential
指标 Index	0 MPa	-0.15 MPa	-0.30 MPa	-0.50 MPa	-0.75 MPa	-1.00 MPa
发芽率Germination percentage （%）	100.00±0.00a	91.00±3.00a	80.00±5.00ab	70.00±4.00ab	58.00±4.00b	42.00±5.00b
出苗率Emergence percentage （%）	100.00±0.00a	91.00±2.00a	79.00±1.00a	67.00±2.00a	41.00±3.00b	33.00±2.00b
发芽指数Germination index	90.82±1.54a	72.91±2.05ab	58.47±2.67b	48.82±1.33bc	36.57±0.75c	30.07±0.39c
活力指数Vigor index	1246.05±2.59a	993.76±3.67ab	700.47±4.42b	504.80±3.95b	331.69±2.16c	220.12±1.97d

Table 2 Effects of rewatering after drought stress on seed germination and emergence

指标 Index	环境水势Environmental water potential
指标 Index	0 MPa	-0.15 MPa	-0.30 MPa	-0.50 MPa	-0.75 MPa	-1.00 MPa
发芽率Germination percentage （%）	0.00±0.00d	6.00±0.15c	11.00±1.75b	18.00±2.25a	14.00±1.25ab	14.00±0.75ab
出苗率Emergence percentage （%）	0.00±0.00d	6.00±0.10c	11.00±0.65b	18.00±1.55a	14.00±0.85ab	14.00±0.35ab
发芽指数Germination index	0.00±0.00d	8.08±0.49c	13.55±0.78b	24.69±0.93a	16.61±0.62ab	16.50±0.57ab
活力指数Vigor index	0.00±0.00d	105.77±1.17c	183.60±1.34b	304.67±1.49a	204.97±1.03ab	180.35±0.82b

Table 3 Effects of drought stress on root length and bud length of E. nutans seedlings

指标 Index	环境水势 Environmental water potential
指标 Index	0 MPa	-0.15 MPa	-0.30 MPa	-0.50 MPa	-0.75 MPa	-1.00 MPa
根长Root length （cm）	6.80±0.23a	7.39±0.31a	6.62±0.19a	6.07±0.35a	5.79±0.47a	5.11±0.26a
芽长Bud length （cm）	6.92±0.39a	6.25±0.27a	5.36±0.24a	4.24±0.41ab	3.28±0.50b	2.26±0.33b
根芽比Root/bud	0.98±0.14b	1.18±0.17b	1.22±0.23b	1.43±0.20b	1.77±0.26ab	2.26±0.21a

Table 4 Effects of drought stress on fresh and dry weight of E. nutans seedlings

指标 Index	环境水势Environmental water potential
指标 Index	0 MPa	-0.15 MPa	-0.30 MPa	-0.50 MPa	-0.75 MPa	-1.00 MPa
根（鲜重） Root fresh weight （g·10 plant^-1）	0.1323a	0.1467a	0.1264a	0.1093ab	0.0971ab	0.0744b
芽（鲜重） Bud fresh weight （g·10 plant^-1）	0.2459a	0.2338ab	0.2169ab	0.1794ab	0.1635b	0.1463b
根（干重） Root dry weight （g·10 plant^-1）	0.0207a	0.0256a	0.0194a	0.0139ab	0.0107b	0.0048c
芽（干重） Bud dry weight （g·10 plant^-1）	0.0333a	0.0293ab	0.0262ab	0.0201b	0.0183b	0.0154b
干物质积累率Dry matter accumulation percentage （%）	0.14±0.01a	0.14±0.02a	0.13±0.01ab	0.11±0.04ab	0.10±0.01b	0.09±0.00b

Table 5 Effects of rewatering after drought stress on root length and bud length of E. nutans seedlings

指标 Index	环境水势Environmental water potential
指标 Index	0 MPa	-0.15 MPa	-0.30 MPa	-0.50 MPa	-0.75 MPa	-1.00 MPa
根长Root length （cm）	0.00±0.00b	6.98±0.66a	6.77±0.59a	6.54±0.47a	6.25±0.51a	5.94±0.41a
芽长Bud length （cm）	0.00±0.00b	8.32±0.79a	8.04±1.02a	7.69±1.21a	7.54±1.33a	7.39±0.92a
根芽比Root/bud	0.00±0.00b	0.84±0.01a	0.84±0.02a	0.85±0.01a	0.83±0.01a	0.82±0.03a

Table 6 Effects of rewatering after drought stress on dry and fresh weight of E. nutans seedlings

指标 Index	环境水势Environmental water potential
指标 Index	0 MPa	-0.15 MPa	-0.30 MPa	-0.50 MPa	-0.75 MPa	-1.00 MPa
根（鲜重） Root fresh weight （g·10 plant^-1）	0.0000b	0.1392a	0.1336a	0.1278a	0.1195a	0.1170a
芽（鲜重） Bud fresh weight （g·10 plant^-1）	0.0000c	0.3144a	0.3114ab	0.2079b	0.2056b	0.2035b
根（干重） Root dry weight （g·10 plant^-1）	0.0000c	0.0251a	0.0224ab	0.0196ab	0.0163b	0.0124b
芽（干重） Bud dry weight （g·10 plant^-1）	0.0000b	0.0394a	0.0371a	0.0359a	0.0347a	0.0333a
干物质积累率Dry matter accumulation percentage （%）	0.00±0.00b	0.14±0.01a	0.14±0.02a	0.14±0.01a	0.14±0.02a	0.14±0.03a

Table 7 Relationship between water absorption time and germination percentage of 50% seeds population

环境水势 Environmental water potential	拟合方程 Fitting equation	相关系数 Correlation coefficient （r）	发芽时间 Germination time （h）
0 MPa	$P i = 1.67 l o g t - 2.65$	0.97	76.95
-0.15 MPa	$P i = 1.33 l o g t - 2.12$	0.95	93.31
-0.30 MPa	$P i = 1.17 l o g t - 1.91$	0.96	114.77
-0.50 MPa	$P i = 1.00 l o g - 1.63$	0.96	136.45
-0.75 MPa	$P i = 0.83 l o g t - 1.34$	0.88	164.76
-1.00 MPa	$P i = 0.67 l o g t - 1.09$	0.88	236.12

Table 7 Relationship between water absorption time and germination percentage of 50% seeds population

环境水势 Environmental water potential	拟合方程 Fitting equation	相关系数 Correlation coefficient （r）	发芽时间 Germination time （h）
0 MPa	$P i = 1.67 l o g t - 2.65$	0.97	76.95
-0.15 MPa	$P i = 1.33 l o g t - 2.12$	0.95	93.31
-0.30 MPa	$P i = 1.17 l o g t - 1.91$	0.96	114.77
-0.50 MPa	$P i = 1.00 l o g - 1.63$	0.96	136.45
-0.75 MPa	$P i = 0.83 l o g t - 1.34$	0.88	164.76
-1.00 MPa	$P i = 0.67 l o g t - 1.09$	0.88	236.12

Table 8 Relationship between germination time and water potential of 50% seeds population

材料Material	拟合方程Fitting equation	相关系数Correlation coefficient （r）	临界水势Critical water potential （MPa）
垂穗披碱草E. nutans	1/t=0.0153ψ_w+0.0130	0.85	-0.85

Table 9 Relationship between water absorption time and emergence percentage of 50% seeds population

环境水势 Environmental water potential	拟合方程 Fitting equation	相关系数 Correlation coefficient （r）	发芽时间 Emergence time （h）
0 MPa	$P i = 1.56 l o g t - 2.46$	0.97	78.96
-0.15 MPa	$P i = 1.22 l o g t - 1.96$	0.95	103.84
-0.30 MPa	$P i = 1.17 l o g t - 1.92$	0.96	117.05
-0.50 MPa	$P i = 0.94 l o g t - 1.53$	0.96	144.39
-0.75 MPa	$P i = 0.72 l o g t - 1.17$	0.88	208.66
-1.00 MPa	$P i = 0.61 l o g t - 0.99$	0.88	277.09

Table 9 Relationship between water absorption time and emergence percentage of 50% seeds population

环境水势 Environmental water potential	拟合方程 Fitting equation	相关系数 Correlation coefficient （r）	发芽时间 Emergence time （h）
0 MPa	$P i = 1.56 l o g t - 2.46$	0.97	78.96
-0.15 MPa	$P i = 1.22 l o g t - 1.96$	0.95	103.84
-0.30 MPa	$P i = 1.17 l o g t - 1.92$	0.96	117.05
-0.50 MPa	$P i = 0.94 l o g t - 1.53$	0.96	144.39
-0.75 MPa	$P i = 0.72 l o g t - 1.17$	0.88	208.66
-1.00 MPa	$P i = 0.61 l o g t - 0.99$	0.88	277.09

Table 10 Relationship between emergence time and water potential of 50% seeds population

材料Material	拟合方程Fitting equation	相关系数Correlation coefficient （r）	临界水势Critical water potential （MPa）
垂穗披碱草E. nutans	1/t=0.0207ψ_w+0.0127	0.90	-0.61

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