The Community Land Model (CLM) started to incorporate crop growth models since version 4.0 in 2012. Since then, the crop model in CLM has been evolved remarkably, but some of the key crop growth responses to environmental conditions (such as the elevated CO₂) have not been well validated. Here, we set up single point simulations with CLM (version 4.5) and validated spring wheat growth response against the Maricopa spring wheat Free Air CO₂ Enrichment (FACE) experiment that consisted of multiyear paired treatments to understand the growth response to elevated CO₂, irrigation, nitrogen fertilization, and their interactions. Overall, CLM showed too positive growth response to elevated CO₂ but insufficient growth response to irrigation. The overestimated growth response to elevated CO₂ may be due to ignoring factors (e.g., leaf traits) that will limit crop growth under elevated CO₂. The insufficient response to irrigation is due to CLM simulating lower latent heat flux during April and May, which resulted in higher soil moisture. In response to nitrogen fertilization, CLM underestimated leaf area index increase but overestimated grain yield increase. In terms of energy fluxes, CLM showed decreased latent heat flux in response to elevated CO₂ but increased latent heat flux in response to nitrogen fertilization, but the response magnitude was much smaller than the observations. Based on these validations, we summarized further model developments for CLM to better simulate crop growth process.

中文翻译：

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在社区土地模型4.5中验证春小麦对CO2升高，灌溉和氮肥响应的响应

自2012年版本4.0起，社区土地模型（CLM）就开始纳入作物生长模型。此后，CLM中的作物模型有了显着的发展，但是某些作物对环境条件的主要响应（例如升高的CO ₂）尚未得到充分验证。在这里，我们使用CLM（版本4.5）进行了单点模拟，并针对Maricopa春季小麦自由空气CO ₂富集（FACE）实验验证了春季小麦的生长响应，该实验由多年配对处理组成，以了解对升高的CO ₂的生长响应，灌溉，氮肥及其相互作用。总体而言，CLM对CO ₂升高的生长反应过于积极但是对灌溉的生长反应不足。高估对CO _2的生长反应可能是由于忽略了在CO ₂升高下会限制作物生长的因素（例如，叶片性状）。对灌溉的响应不足是由于CLM模拟了4月和5月较低的潜热通量，导致土壤湿度较高。响应氮肥，CLM低估了叶面积指数，但高估了谷物产量。在能量通量方面，CLM显示出响应于升高的CO ₂潜热通量降低但是响应氮肥增加了潜热通量，但是响应幅度比观测值小得多。基于这些验证，我们总结了CLM的进一步模型开发，以更好地模拟作物生长过程。