Root responses to elevated CO2, warming and irrigation in a semi‐arid grassland: Integrating biomass, length and life span in a 5‐year field experiment
Root responses to elevated CO2, warming and irrigation in a semi‐arid grassland: Integrating biomass, length and life span in a 5‐year field experiment
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DOI：
10.1111/1365-2745.12993
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发表时间：
2018-11
影响因子：
5.5
通讯作者：
K. Mueller;D. Lecain;M. L. McCormack;E. Pendall;M. Carlson;D. Blumenthal
中科院分区：
文献类型：
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作者：
K. Mueller;D. Lecain;M. L. McCormack;E. Pendall;M. Carlson;D. Blumenthal
植物根系介导环境变化对生态系统的影响，但由于很少有实验评估多种环境因素及其相互作用，因此对根系对环境变化的响应的认识有限。根函数的推断也很有限，因为很少测量根长度动态。通过5年的混合草地试验，我们报告了根系生物量、长度和寿命对二氧化碳浓度升高、变暖、二氧化碳和变暖联合升高以及灌溉的响应。采用土芯法对根系生物量进行量化，采用微型植管法对根系长度动态进行评价。通过比较根系动态与已发表的土壤资源和地上生产力结果，我们提供了气候变化如何影响草地生态系统的机制见解。在表层0 ~ 15 cm深度，灌溉和CO2浓度升高均使根系总长度增加2倍，但灌溉使根系生物量减少，CO2浓度升高对根系生物量的正向影响较小。灌溉和二氧化碳浓度升高对总根长有显著的正向影响，这是由于根长产量和根寿命都增加了。灌水和CO2浓度升高导致根系总长度和寿命增加，与植物生长由限水向限氮的转变相一致。单独变暖对这一浅层土壤根系生物量、长度和寿命的影响很小。升温和升高的CO2联合处理使根生物量和总根长增加了约25%，但如果CO2和升温是单独作用的，则该处理的总根长低于预期。处理对根长和寿命的影响随土壤深度和根径的不同而不同。合成。二氧化碳和气候变暖的亚加性效应表明，单独研究二氧化碳浓度升高可能高估了草地根系未来获取资源的能力。在这片混草草原中，二氧化碳浓度升高和气候变暖刺激了深层土壤的总根长和根寿命，可能增加了植物对更稳定的生长限制资源池的获取，包括水和磷。因此，这些根系响应有助于解释在这些预估气候条件下先前观测到的更高、更稳定的地上生产力。
Plant roots mediate the impacts of environmental change on ecosystems, yet knowledge of root responses to environmental change is limited because few experiments evaluate multiple environmental factors and their interactions. Inferences about root functions are also limited because root length dynamics are rarely measured. Using a 5‐year experiment in a mixed‐grass prairie, we report the responses of root biomass, length and life span to elevated carbon dioxide (CO2), warming, elevated CO2 and warming combined, and irrigation. Root biomass was quantified using soil cores and root length dynamics were assessed using minirhizotrons. By comparing root dynamics with published results for soil resources and above‐ground productivity, we provide mechanistic insights into how climate change might impact grassland ecosystems. In the upper soil layer, 0–15 cm depth, both irrigation and elevated CO2 alone increased total root length by twofold, but irrigation decreased root biomass and elevated CO2 had only small positive effects on root biomass. The large positive effects of irrigation and elevated CO2 alone on total root length were due to increases in both root length production and root life span. The increased total root length and life span under irrigation and elevated CO2 coincided with apparent shifts from water limitation of plant growth to nitrogen limitation. Warming alone had minimal effects on root biomass, length and life span in this shallow soil layer. Warming and elevated CO2 combined increased root biomass and total root length by c. 25%, but total root length in this treatment was lower than expected if the effects of CO2 and warming alone were additive. Treatment effects on total root length and root life span varied with soil depth and root diameter. Synthesis. Sub‐additive effects of CO2 and warming suggest studies of elevated CO2 alone might overestimate the future capacity of grassland root systems to acquire resources. In this mixed‐grass prairie, elevated CO2 with warming stimulated total root length and root life span in deeper soils, likely enhancing plant access to more stable pools of growth‐limiting resources, including water and phosphorus. Thus, these root responses help explain previous observations of higher, and more stable, above‐ground productivity in these projected climate conditions.