In order to accurately estimate the carbon (C) balance in arid and semi-arid grasslands, it is necessary to first understand how the demands of photosynthates and root carbon (C) are allocated in response to drought. To accomplish this goal, we used a ¹³C pulse labeling technique to assess correlations between root morphology and the amount of ¹³C in the root, which is a measure of respiration. We compared respiration changes via the excised root ¹³C of Bothriochloa ischaemum at various root excision times (i.e., 0, 6, 24, 48, 216, and 360 h after labeling). Our results showed that ¹³C and root respiration continued to increase until 216 h after labeling, and then they decreased after 360 h. Root respiration correlated significantly with the carbon labeled as being from the fine roots that were undergoing drought stress treatments. This indicates that later-photosynthates are the primary C source for root respiration. Fine root ¹³C positively correlated with fine root biomass and specific root length under serious drought conditions. This suggests that fine root growth is based primarily on recently derived photosynthates. Serious drought was shown to inflate the root/shoot ratio by increasing both the ¹³C and the biomass, which led to greater C allocation in the root system. Finally, the fine/coarse root ratios of ¹³C and biomass were greatest in the serious drought treatment. This suggests that fine roots have a higher C demand than coarse roots under drought stress. Fine root respiration was also found to stimulate new C demand in roots because the amount of ¹³C created during root respiration was positively correlated with tissue N concentration of fine roots.

为了准确估计干旱和半干旱草原的碳（C）平衡，有必要首先了解如何响应干旱分配光合产物和根系碳（C）的需求。为了实现此目标，我们使用了¹³ C脉冲标记技术来评估根部形态与根中¹³ C量之间的相关性，这是呼吸的一种度量。我们比较了在不同的根切除时间（即标记后的0、6、24、48、216和360 h），通过剪枝Both的根¹³ C呼吸变化。我们的结果表明¹³碳和根的呼吸持续增加直到标记后216 h，然后在360 h之后下降。根呼吸与标记为来自经历干旱胁迫处理的细根的碳显着相关。这表明后期的光合产物是根呼吸的主要碳源。在严重干旱条件下，细根¹³ C与细根生物量和特定根长呈正相关。这表明良好的根生长主要基于最近衍生的光合产物。结果表明，严重的干旱会通过增加¹³ C和生物量来增加根/茎比，从而增加根系中的C分配。最后，粗/粗比为¹³严重干旱处理中碳和生物量最大。这表明在干旱胁迫下，细根对碳的需求高于粗根。还发现细根呼吸可刺激根中的新碳需求，因为根呼吸期间产生的¹³ C的量与细根的组织N浓度呈正相关。