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Turgor-limited predictions of tree growth, height and metabolic scaling over tree lifespans
Tree Physiology ( IF 4 ) Pub Date : 2021-07-22 , DOI: 10.1093/treephys/tpab094
Aaron Potkay 1 , Teemu Hölttä 2 , Anna T Trugman 3 , Ying Fan 1
Affiliation  

Abstract
Increasing evidence suggests that tree growth is sink-limited by environmental and internal controls rather than by carbon availability. However, the mechanisms underlying sink-limitations are not fully understood and thus not represented in large-scale vegetation models. We develop a simple, analytically solved, mechanistic, turgor-driven growth model (TDGM) and a phloem transport model (PTM) to explore the mechanics of phloem transport and evaluate three hypotheses. First, phloem transport must be explicitly considered to accurately predict turgor distributions and thus growth. Second, turgor-limitations can explain growth-scaling with size (metabolic scaling). Third, turgor can explain realistic growth rates and increments. We show that mechanistic, sink-limited growth schemes based on plant turgor limitations are feasible for large-scale model implementations with minimal computational demands. Our PTM predicted nearly uniform sugar concentrations along the phloem transport path regardless of phloem conductance, stem water potential gradients and the strength of sink-demands contrary to our first hypothesis, suggesting that phloem transport is not limited generally by phloem transport capacity per se but rather by carbon demand for growth and respiration. These results enabled TDGM implementation without explicit coupling to the PTM, further simplifying computation. We test the TDGM by comparing predictions of whole-tree growth rate to well-established observations (site indices) and allometric theory. Our simple TDGM predicts realistic tree heights, growth rates and metabolic scaling over decadal to centurial timescales, suggesting that tree growth is generally sink and turgor limited. Like observed trees, our TDGM captures tree-size- and resource-based deviations from the classical ¾ power-law metabolic scaling for which turgor is responsible.


中文翻译:

对树木生长、高度和代谢尺度在树木寿命期间的限制性预测

摘要
越来越多的证据表明,树木的生长受环境和内部控制的限制,而不是受碳可用性的限制。然而,汇限制的潜在机制尚未完全了解,因此未在大型植被模型中表示。我们开发了一个简单的、解析求解的、机械的、膨压驱动的生长模型 (TDGM) 和韧皮部运输模型 (PTM) 来探索韧皮部运输的机制并评估三个假设。首先,必须明确考虑韧皮部运输以准确预测膨压分布和生长。其次,膨压限制可以解释生长比例与大小(代谢比例)。第三,膨压可以解释现实的增长率和增量。我们展示了这种机制,基于植物膨压限制的汇限制增长方案对于具有最小计算需求的大规模模型实现是可行的。我们的 PTM 预测沿韧皮部运输路径几乎均匀的糖浓度,无论韧皮部电导率、茎水势梯度和汇需求的强度与我们的第一个假设相反,这表明韧皮部运输通常不受韧皮部运输能力本身的限制,而是增长和呼吸的碳需求。这些结果在没有显式耦合到 PTM 的情况下实现了 TDGM,进一步简化了计算。我们通过将全树生长率的预测与公认的观察结果(站点指数)和异速生长理论进行比较来测试 TDGM。我们简单的 TDGM 预测现实的树高,十年到百年时间尺度的生长速率和代谢比例,表明树木生长通常是下沉和膨胀受限的。像观察到的树一样,我们的 TDGM 捕获了与 turgor 负责的经典 ¾ 幂律代谢尺度的基于树大小和资源的偏差。
更新日期:2021-07-22
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