Effects of extreme drought and extreme precipitation on aboveground productivity of ephemeral plants across different slope positions along sand dunes

doi:10.17521/cjpe.2021.0473

Abstract

Abstract:

Aims In recent years, the frequency of extreme drought and extreme precipitation events in arid and semi-arid regions is increasing, which has a profound impact on ecosystem productivity and carbon cycling. In desert ecosystems, vegetation is sensitive to precipitation changes, but the differences in sensitivity of aboveground productivity of ephemeral plants to extreme drought and extreme precipitation, and the moderating effect of slope positions on them need to be further studied.

Methods In this study, we experimentally reduced and increased precipitation amounts by 65% during two consecutive growing seasons in situ across four different slope positions (the bottom of the sand dune facing west (BW), the middle of the sand dune facing west (MW), the middle of the sand dune facing east (ME), and the bottom of the sand dune facing east (BE)) along sand dunes in the southern edge of the Gurbantünggüt Desert. We analyzed the sensitivity of aboveground productivity of ephemeral plants to extreme drought and extreme precipitation, and discussed the synergistic effect of slope position factors and the driving mechanism of aboveground productivity of ephemeral plants.

Important findings The results showed that: (1) Overall, the relationship between aboveground net primary productivity (ANPP) of ephemeral plants and precipitation in growing season was asymmetric, and the ANPP was more sensitive to extreme drought than to extreme precipitation. (2) Specifically, the relationship between precipitation and ANPP of ephemeral plants at BW, MW, and BE were non-linear, i.e., the rate of increase in ANPP decreases with the increased precipitation; The existence of two dominant species in the middle of the sand dune facing east changed the relationship between aboveground productivity and precipitation in the growing season, and the relationship between them showed a positive linear relationship. (3) In addition, the density of ephemeral plants (the sum of all species density) had the greatest direct impact on aboveground productivity of ephemeral plants, suggesting that extreme drought resulted in physiological death of ephemeral plants and reduced aboveground productivity by reducing plant density, while extreme precipitation increased population density to overcome meristem constraints and improve aboveground productivity. This study provides a scientific basis for accurately assessing the dynamics of carbon cycle in desert ecosystems under the background of frequent extreme climate events.

Key words: net primary productivity, ephemeral plants, extreme drought, extreme precipitation, sensitivity, slope position, the Gurbantünggüt Desert

ZANG Yong-Xin, MA Jian-Ying, ZHOU Xiao-Bing, TAO Ye, YIN Ben-Feng, Shayaguli JIGEER, ZHANG Yuan-Ming. Effects of extreme drought and extreme precipitation on aboveground productivity of ephemeral plants across different slope positions along sand dunes[J]. Chin J Plant Ecol, 2022, 46(12): 1537-1550.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2021.0473

https://www.plant-ecology.com/EN/Y2022/V46/I12/1537

Figures/Tables 8

Fig. 1 Study site and experimental design. BE, bottom of sand dune facing east; BW, bottom of sand dune facing west; ME, middle of sand dune facing east; MW, middle of sand dune facing west.

Fig. 2 Probability distribution of ephemeral plants growing season precipitation during the last 100 years for the southern edge of the Gurbantünggüt Desert (A) and effects of extreme drought and precipitation treatments on mean growing season soil water content (B)(mean ± SE). BE, bottom of sand dune facing east; BW, bottom of sand dune facing west; ME, middle of sand dune facing east; MW, middle of sand dune facing west. Different lowercase letters indicates significant differences between precipitation treatments of same slope position (p < 0.05); different uppercase letters indicate significant differences between different slope positions in the same precipitation treatment (p < 0.05).

Table 1 Generalized linear mixed model results for the effects of precipitation change (P), sand dune slope positions (Sp), year (Y), and their interactive effects on soil water content (SWC) and sensitivity of aboveground net primary productivity (ANPP) of ephemeral plants

效应 Effect	土壤含水量 SWC		ANPP敏感性 ANPP sensitivity
效应 Effect	df	F	df	F
降水处理 P	2	53.15^**	1	3.05
坡向坡位 Sp	3	5.54^*	3	1.31
年份 Y	1	49.59^**	1	8.53^**
降水处理×坡向坡位 P × Sp	6	43.65^**	3	0.52
降水处理×年 P × Y	2	0.38	1	0.22
坡向坡位×年 Sp × Y	3	1.75	3	0.48
降水处理×坡向坡位×年 P × Sp × Y	6	0.89	3	0.32

Fig. 3 Sensitivity of aboveground net primary productivity (ANPP) of four sand dune slope positions to extreme drought and precipitation treatments (mean ± SE). BE, bottom of sand dune facing east; BW, bottom of sand dune facing west; ME, middle of sand dune facing east; MW, middle of sand dune facing west.

Fig. 4 Relationship between growing season precipitation and aboveground net primary productivity (ANPP) of ephemeral plants in all and four sand dune slope positions (mean ± SE). BE, bottom of sand dune facing east; BW, bottom of sand dune facing west; ME, middle of sand dune facing east; MW, middle of sand dune facing west.

Table 2 Fitting function of growing season precipitation and aboveground net primary productivity (ANPP) in all and four sand dune slope positions

沙垄不同坡向坡位 Sand dune slope positions	拟合公式 Fitting function	R²	AIC
西坡底部 BW	y = 41.6 - 31.2exp(-(x - 39.8)/81.3)	0.98	4.47
西坡底部 BW	y = 6.79 + 0.28x	0.93	5.76
西坡中部 MW	y = 30.6 - 22.7exp(-(x - 20.0)/55.5)	0.94	6.83
西坡中部 MW	y = 2.04 + 0.23x	0.90	12.98
东坡中部 ME	y = 46.1 - 24.4exp(-(x - 26.3)/57.5)	0.86	10.32
东坡中部 ME	y = 14.8 + 0.25x	0.95	9.25
东坡底部 BE	y = 70.5 - 39.7exp(-(x - 91.9)/218.0)	0.86	5.53
东坡底部 BE	y = 11.86 + 0.17x	0.78	6.75
全部 All	y = 51.4 - 31.8exp(-(x - 20.1)/81.3)	0.71	68.91
全部 All	y = 10.7 + 0.2x	0.44	78.70

Fig. 5 Effects of precipitation treatments on the aboveground net primary productivity (ANPP) of dominant species Erodium oxyrhinchum and Centaurea pulchella (A) and its percentage of ANPP (B) in the middle of sand dune facing east (mean ± SE). * indicates significant differences (p < 0.05) between the ANPP of E. oxyrhinchum and C. pulchella.

Fig. 6 A structural equation model (SEM) representing the effects of soil water content (SWC) on above-ground net primary production (ANPP) in all and four sand dune slope positions. The SEM considered all plausible pathways through which plant traits influence ANPP. Solid lines represent the positive paths, dashed lines indicate negative paths. Line width is proportional to the strength of the relationship. BE, bottom of sand dune facing east; BW, bottom of sand dune facing west; ME, middle of sand dune facing east; MW, middle of sand dune facing west. *, p < 0.05; **, p < 0.01. RMSEA, root mean square error of approximation. R2 represents the proportion of the variance for each dependent variable in the model.

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