Purpose

Impacts of dryness stress (i.e., low soil moisture [SM] and high vapor pressure deficit [VPD]) on gross primary production (GPP) have received considerable attention in recent years, however, their biological mechanism still needs to be elucidated.

Methods

We decomposed GPP into canopy stomatal conductance (gs), ratio of intercellular to atmospheric CO₂ partial pressure (Ci/Ca), and species composition and investigated the interaction of dryness stress, gs, Ci/Ca, and relative abundance of C4 plants (C4/(C3 + C4)) to determine how they regulate GPP along an aridity gradient in Inner Mongolia Plateau. We used biomass-weighted leaf carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes to calculate canopy Ci/Ca and ¹⁸O enrichment in leaf tissue above source water (△¹⁸O), respectively.

Results

A positive relationship between 1/△¹⁸O and canopy gs demonstrated that 1/△¹⁸O was a reliable indicator for canopy gs. Soil moisture (SM) exhibited a positive effect on 1/△¹⁸O and Ci/Ca, while Ci/Ca decreased and C4/(C3 + C4) increased with increasing water vapor pressure (VPD). 1/△¹⁸O and C4/(C3 + C4) indirectly regulated GPP via Ci/Ca, and the effect of C4/(C3 + C4) on the variability in Ci/Ca was stronger than that of 1/△¹⁸O. Interaction between dryness stressors (SM and VPD) and vegetation properties (1/△¹⁸O, Ci/Ca, and C4/(C3 + C4)) captured 74.6% of the variability in GPP, indicating that spatial variability in GPP was determined overwhelmingly by indirect effects of dryness on biological processes.

Conclusions

Increasing relative abundance of C4 plants would effectively mitigate the negative effects of dryness stress on GPP.

中文翻译：

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增加 C4 植物的相对丰度可减轻干旱胁迫对草原生态系统干旱梯度沿线初级生产力的影响

目的

近年来，干旱胁迫（即低土壤水分[ SM ]和高蒸汽压亏缺[ VPD ]）对总初级生产力（GPP）的影响受到了广泛关注，但其生物学机制仍有待阐明。

方法

我们将GPP分解为冠层气孔导度 ( gs )、细胞间与大气 CO ₂分压比 ( Ci/Ca ) 和物种组成，并研究了干旱胁迫、gs、Ci/Ca和C 4 植物相对丰度的相互作用( C 4/( C 3 +  C 4)) 以确定它们如何在内蒙古高原沿干旱梯度调节GPP 。我们使用生物量加权叶片碳 ( δ ¹³ C) 和氧 ( δ ¹⁸ O) 同位素来计算冠层Ci/Ca和¹⁸ O分别在源水以上叶片组织中富集（△ ¹⁸ O）。

结果

1/ △ ¹⁸ O 与冠层gs呈正相关，表明1/ △ ¹⁸ O 是冠层gs的可靠指标。土壤水分（SM ）对1/ △ ¹⁸ O和Ci/Ca有正向影响，而随着水蒸气压（VPD ）的增加， Ci/Ca降低，C 4/( C 3 +  C 4)升高。1/ △ ¹⁸ O 和C 4/( C 3 +  C 4)通过Ci/Ca间接调节GPP, C 4/( C 3 +  C 4) 对Ci/Ca变异性的影响强于 1/ △ ^{18 O. 干旱胁迫 (} SM和VPD ) 与植被特性 (1/ △ ¹⁸ ) 的相互作用O、Ci/Ca和C 4/( C 3 +  C 4)) 捕获了 GPP 中 74.6% 的变异性，表明GPP的空间变异性主要由干燥对生物过程的间接影响决定。

结论

增加C4植物的相对丰度将有效减轻干旱胁迫对GPP的负面影响。