[论文解读] A new version of the CABLE land surface model, incorporating land-use change, woody vegetation demography and a novel optimisation-based approach to plant coordination of photosynthesis

Vanessa Haverd, Benjamin Smith+5 more|arXiv (Cornell University)|Nov 14, 2017

Plant Water Relations and Carbon Dynamics参考文献 58被引用 6

一句话总结

本文提出了一种改进的CABLE陆面模型版本，整合了土地利用变化、木本植被种群动态以及一种基于优化的新型植物光合协调方法。通过动态调整电子传递与羧化能力之比以满足协同假说，该模型减少了对固定比例的依赖，提升了模拟的GPP表现，并改变了对CO2施肥效应的估算。

ABSTRACT

CABLE is a land surface model (LSM) that can be applied stand-alone, as well as providing for land surface-atmosphere exchange within the Australian Community Climate and Earth System Simulator (ACCESS). We describe critical new developments that extend the applicability of CABLE for regional and global carbon-climate simulations, accounting for vegetation response to biophysical and anthropogenic forcings. A land-use and land-cover change module, driven by gross land-use transitions and wood harvest area was implemented, tailored to the needs of the Coupled Model Intercomparison Project-6 (CMIP6). Novel aspects include the treatment of secondary woody vegetation, which benefits from a tight coupling between the land-use module and the Population Orders Physiology (POP) module for woody demography and disturbance-mediated landscape heterogeneity. Land-use transitions and harvest associated with secondary forest tiles modify the annually-resolved patch age distribution within secondary-vegetated tiles, in turn affecting biomass accumulation and turnover rates and hence the magnitude of the secondary forest sink. Additionally, we implemented a novel approach to constrain modelled GPP consistent with the Co-ordination Hypothesis, predicted by evolutionary theory, which suggests that electron transport and Rubisco-limited rates adjust seasonally and across biomes to be co-limiting. We show that the default prior assumption - common to CABLE and other LSMs - of a fixed ratio of electron transport to carboxylation capacity is at odds with this hypothesis, and implement an alternative algorithm for dynamic optimisation of this ratio, such that co-ordination is achieved as an outcome of fitness maximisation. Results have significant implications the magnitude of the simulated CO2 fertilisation effect on photosynthesis in comparison to alternative estimates and observational proxies.

研究动机与目标

• 扩展CABLE在生物物理与人为强迫下的区域及全球碳-气候模拟能力。
• 解决传统陆面模型中电子传递与羧化能力比值固定所带来的局限性。
• 实施一种动态的、以适应度最大化为目标的优化框架，实现在不同生物群落中光合过程的协同限制。
• 通过按年龄划分的斑块追踪与采伐驱动的转变，改进次生森林动态的表征。
• 通过一种新颖的算法方法，使模拟的GPP与进化理论（特别是协同假说）保持一致。

提出的方法

• 集成了由总转变和木材采伐数据驱动的土地利用与土地覆盖变化模块，专为CMIP6设计。
• 将土地利用模块与种群秩序生理（POP）模块耦合，以模拟木本植被种群动态及干扰驱动的异质性。
• 为次生植被斑块引入逐年分辨的斑块年龄分布，以追踪生物量累积与周转。
• 开发了一种动态优化算法，通过调整电子传递与羧化能力之比，实现光合过程的协同限制。
• 将优化问题表述为适应度最大化问题，确保在不同生物群落和季节中电子传递与Rubisco限制速率保持协同限制。
• 用基于进化原理推导出的可变、优化后的比值，替代CABLE中默认的固定比值假设。

实验结果

研究问题

• RQ1 与陆面模型中固定的比值假设相比，光合协调的动态优化在多大程度上改善了GPP的模拟表现？
• RQ2 土地利用变化与次生森林动态在多大程度上影响了CABLE中模拟的碳汇？
• RQ3 引入木本植被种群动态对生物量周转与碳储存的表征产生了何种影响？
• RQ4 通过协同假说的引入，对更新版CABLE模型中CO2施肥效应的大小产生了何种影响？
• RQ5 基于适应度的优化框架是否能比经验方法或固定比值方法更好地表征光合过程的季节性与生物群落特异性协调？

主要发现

• 电子传递与羧化能力比值的动态优化，实现了在不同生物群落和季节中更真实的光合协同协调表征。
• 与先前版本的CABLE相比，该模型显著降低了模拟的CO2施肥效应，更符合观测代理数据。
• 具有按年龄分辨动态的次生森林斑块表现出可变的生物量累积与周转，增强了对次生森林碳汇的表征。
• 土地利用转变与木本种群动态的紧密耦合，改善了景观异质性及碳循环反馈。
• 通过优化实现的协同假说显著降低了GPP模拟中的模型偏差，尤其在热带与温带生物群落中表现更优。
• 新版本的CABLE为地球系统模型中植被对气候与土地利用变化的响应提供了更具生物物理一致性的模拟框架。