Divergent climate feedbacks in the growing period and the dormancy period to sowing date shift of winter wheat in the North China Plain

Abstract

Abstract. The land cover and management changes have strong feedbacks to climate through surface biophysical and biochemical processes. Agricultural phenology dynamic exerted measurable impacts on land surface properties, biophysical process and climate feedback in particular times at local/regional scale. But the responses of climate feedback through surface biophysical process to sowing date shift in the winter wheat ecosystem have been overlooked, especially at winter dormancy period. Considering the large cultivation area, unique surface property and phenology shift of winter wheat in the North China Plain, we first validated the SiBcrop model. Then, we used it to investigate the dynamics of leaf area index (LAI) and canopy temperature (Tc) under two planting date scenarios (Early Sowing: EP; Late Sowing: LP) of winter wheat at 10 selected stations. Finally, the surface energy budget was analyzed and interpreted. The results showed that the SiBcrop with a modified crop phenology scheme better simulated the seasonal dynamic of LAI, Tc, phenology, and surface heat fluxes. Earlier sowing date had higher LAI with earlier development than later sowing date. But the response of Tc to sowing date exhibited opposite patterns during the dormancy and active growth periods: EP led to higher Tc (0.05 K) than LP in the dormancy period and lower Tc (−0.2 K) in the growth period. The highest difference (0.6 K) between EP and LP happened at the time when wheat was sown in EP but wasn't in LP. The higher LAI captured more net radiation with lower surface albedo for warming, whist surface energy partitioning exerted cooling effect. The relative contributions of albedo-radiative process and partitioning-non-radiative process determined the climate effect of sowing date shift. The spatial pattern of the climate response to sowing date was influence by precipitation and air temperature. The study highlight that the climate effects of the sowing date shift in winter dormancy period are worthy of attention.

Impacts of maize planting date and variety on canopy temperature on the North China Plain and surface biophysical mechanism

“…和-20 W•m -2 [12] ； 提前播种造成 6 月份 LH 增强， SH 降低， 成熟期到收获期的缩短增强了 10 月份净辐射 (Rn) [8] ； 地表反照率(α)在玉米的不同生育期(发芽、 开 花和成熟等)存在差异， 并受种植日期影响 [13] 。农田 地表特征变化通过地表生物物理过程的气候效应， 主要归因于地表辐射机制和地表能量分配机制。 地表辐射机制与地表反照率变化引起的净辐射动 态有关； 地表能量分配机制涉及净辐射在潜热和感 热之间的分配。地表反照率降低引起净辐射吸收 的增加， 有利于温度升高； 净辐射分配到潜热比例 的增加有利于降温。观测数据 [3] 及模型模拟结果 [12] 表明， 温带地区农业物候期延长的地表生物物理 过程通常表现出地表能量分配-冷却效应超过地 表反照率-升温效应， 造成物候期变化总体以降温 为主 [9] 。 玉米物候期变化通过地表生物物理过程对特 定时间的气候产生了可检测的影响 [9] 。但是相关的 研究集中在美国玉米带 [8,12] ， 华北平原主要关注冬小 麦-玉米轮作系统在间种期的气候反馈 [11,14] 水分利用效率的玉米单作成为潜在的重要选项 [15] ， 使用长生长期的玉米品种对于充分利用增长的农业 气候资源和增加产量意义重大 [16] mm 之间波动 [19] 。土壤类型为沙壤土 [18] 单生物圈模型 [21] 。通过耦合玉米、 大豆、 春小麦和 冬小麦的生长子程序， SiBcrop 模型可以较好地模 拟农田生态系统中地表热量、 水分、 动量和气体等 过程 [21][22][23] 。 模型中玉米的播种期受气温的控制， 气温连续 7 d 超过 13.9 ℃的则播种。GDD 是玉米生长过程 中的关键参数， 决定了玉米的生育期、 生物量积 累和分配。分配到叶片的有机物根据比叶面积转 换为 LAI， 进而参与到地表能量和水分交换过程 的计算 [24][25] 。 优化玉米生长模型显著提高了 SiBcrop 模型对 华北平原玉米生长和地表水热平衡的模拟效果 [22] 。 玉米生长模型的优化包括： ① 物候期的调整。播种 22] ， 与其他陆面过程模型的模拟 误差相似 [26][27] 。可见， SiBcrop 模型具有较强的适应 能力， 优化后可以较好模拟华北平原农田生态系统 的陆面过程动态。…”