Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest
Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest
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DOI：
10.1111/1365-2745.13022
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发表时间：
2019-01-01
影响因子：
5.5
通讯作者：
Oliveira, Rafael S.
中科院分区：
文献类型：
--
作者：
Brum, Mauro;Vadeboncoeur, Matthew A.;Oliveira, Rafael S.
1. 根系深度和地上水力特征之间的关系可以潜在地定义抗旱策略，这对于确定季节性热带森林中的物种分布和共存非常重要，并且了解这一点对于预测未来气候变化对这些生态系统的影响也很重要。2。我们使用从不同深度的树木木质部和土壤中收集的水的稳定同位素比（δ O-18 和δ H-2）评估了亚马逊季节性森林中 12 种主要树种（约占森林断面积的 42%）的根部深度。我们利用 2015/2016 年与 ENSO 相关的重大干旱，导致土壤中同位素大量蒸发，并揭示了极端条件下每个物种的用水策略。我们测量了正常年（2014 年；Psi（非 ENSO））和极端干旱年（2015 年；Psi（ENSO））的最小旱季叶水势。此外，我们测量了木质部水力特征，这些特征表明树木在没有水力衰竭风险的情况下耐受的水势阈值（P-50 和 P-88）。3。我们证明，共存的树木很大程度上沿着由根深差异、光照和低水势耐受性定义的单一水文生态位轴隔离。这些生根深度的差异与树木的大小密切相关。胸径 (DBH) 解释了 Delta O-18（木质部）变异的 72%。此外，δ O-18（木质部）解释了 P-50 变化的 49% 和 P-88 变化的 70%，浅根物种更能耐受低水势，而木质部水的 δ O-18 解释了最小 Psi（非 ENSO）和 Psi（ENSO）变化的 47% 和 77%。4。我们提出了一种新的公式来估计有效的功能性根深，即根可以维持生理功能吸水的可能土壤深度，使用胸径作为该地点根深度的预测因子。根据这些估计，我们得出结论，塔帕霍斯森林中最丰富的科、属和物种的根系深度存在系统性差异，尤其是林下物种的根系深度仅限于浅5。我们的结果支持了水文生态位隔离理论及其与抗旱性相关的潜在权衡，这也影响了亚马逊东部季节性森林中树木的优势结构。6。合成。我们的结果支持水文生态位隔离理论，并证明了其与抗旱性相关的潜在权衡（获得深水与容忍极低水势）。我们发现，定义用水特征的单一水文轴与树木大小密切相关，并推断周期性极端干旱会影响亚马逊东部季节性森林中树木的群落组成和优势结构。
1. The relationship between rooting depth and above-ground hydraulic traits can potentially define drought resistance strategies that are important in determining species distribution and coexistence in seasonal tropical forests, and understanding this is important for predicting the effects of future climate change in these ecosystems.2. We assessed the rooting depth of 12 dominant tree species (representing c. 42% of the forest basal area) in a seasonal Amazon forest using the stable isotope ratios (delta O-18 and delta H-2) of water collected from tree xylem and soils from a range of depths. We took advantage of a major ENSO-related drought in 2015/2016 that caused substantial evaporative isotope enrichment in the soil and revealed water use strategies of each species under extreme conditions. We measured the minimum dry season leaf water potential both in a normal year (2014; Psi(non-ENSO)) and in an extreme drought year (2015; Psi(ENSO)). Furthermore, we measured xylem hydraulic traits that indicate water potential thresholds trees tolerate without risking hydraulic failure (P-50 and P-88).3. We demonstrate that coexisting trees are largely segregated along a single hydrological niche axis defined by root depth differences, access to light and tolerance of low water potential. These differences in rooting depth were strongly related to tree size; diameter at breast height (DBH) explained 72% of the variation in the delta O-18(xylem). Additionally, delta O-18(xylem) explained 49% of the variation in P-50 and 70% of P-88, with shallow-rooted species more tolerant of low water potentials, while delta O-18 of xylem water explained 47% and 77% of the variation of minimum Psi(non-ENSO) and Psi(ENSO).4. We propose a new formulation to estimate an effective functional rooting depth, i.e. the likely soil depth from which roots can sustain water uptake for physiological functions, using DBH as predictor of root depth at this site. Based on these estimates, we conclude that rooting depth varies systematically across the most abundant families, genera and species at the Tapajos forest, and that understorey species in particular are limited to shallow rooting depths.5. Our results support the theory of hydrological niche segregation and its underlying trade-off related to drought resistance, which also affect the dominance structure of trees in this seasonal eastern Amazon forest.6. Synthesis. Our results support the theory of hydrological niche segregation and demonstrate its underlying trade-off related to drought resistance (access to deep water vs. tolerance of very low water potentials). We found that the single hydrological axis defining water use traits was strongly related to tree size, and infer that periodic extreme droughts influence community composition and the dominance structure of trees in this seasonal eastern Amazon forest.