Beechey-Gradwell Zac, Mackay Alec, Condron Leo, Bowatte Saman, Agrelo Florencia De Lucca, Brock Shona, Thompson Danica, Theobald Phil, Lieffering Mark, Shi Shengjing, Villamizar Laura, Newton Paul
AgResearch Ltd, Climate Change and Forage Innovations, Palmerston North, New Zealand.
Agriculture and Life Sciences, Lincoln University, Christchurch, New Zealand.
Glob Chang Biol. 2025 Apr;31(4):e70150. doi: 10.1111/gcb.70150.
Phosphorus (P) is a finite resource and an essential macronutrient for plant growth. The importance of low soil P availability in constraining plant biomass responses to elevated CO (eCO) is increasingly recognized. P fertilization could alleviate these constraints, but biogeochemical feedbacks under eCO may diminish the effectiveness of P fertilizer in raising soil P availability. Here, we present data from a botanically diverse grazed pasture enriched with CO (+84-111 ppm) and supplied with P fertilizer (1.5 g P m year) for approximately 24 years, showing (1) a sustained 27% reduction in topsoil Olsen P under eCO prior to annual fertilizer application, and (2) an approximate halving of the short-term (approximately 4 months) effectiveness of P fertilizer in raising Olsen P by 1 unit under eCO. Similar results occurred with the Bray-1 soil P test. These effects soon disappeared after CO enrichment stopped. Accumulation of moderately labile organic P in the eCO topsoil shortly after fertilization indicated rapid biological immobilization of newly applied P occurring under eCO. Alternative P loss mechanisms under eCO, including inorganic P depletion due to increased pasture growth, increased P offtake versus return through the plant→animal→dung pathway, or P movement down the soil profile, were not supported by the available evidence. Despite this, pasture P concentration and uptake were similar under eCO and ambient CO, and the biomass of the P-sensitive legume Trifolium repens was often greater under eCO. Thus, either the fertilizer regime was sufficient to maintain a non-limiting pasture P status, or integrated plant-soil biological adjustments under eCO compensated for reduced P availability. If compensatory mechanisms play a greater role in supporting crop P nutrition under eCO but are neglected by routine soil P availability tests focused on inorganic P, overapplication of P fertilizers will occur as CO levels continue to rise.
磷（P）是一种有限的资源，也是植物生长必需的大量营养素。土壤有效磷含量低对植物生物量对升高的二氧化碳（eCO）响应的限制作用，正日益受到人们的认识。磷肥可以缓解这些限制，但eCO条件下的生物地球化学反馈可能会降低磷肥提高土壤有效磷的效果。在这里，我们展示了来自一个植物种类多样的放牧牧场的数据，该牧场在大约24年的时间里，二氧化碳浓度升高（+84 - 111 ppm）并施用磷肥（1.5 g P m² 年），结果表明：（1）在每年施肥前，eCO条件下表层土壤有效磷（Olsen P）持续降低27%；（2）在eCO条件下，磷肥使有效磷提高1个单位的短期（约4个月）效果大约减半。Bray - 1土壤磷测试也得到了类似结果。二氧化碳浓度升高停止后，这些影响很快消失。施肥后不久，eCO表层土壤中中度不稳定有机磷的积累表明，在eCO条件下新施磷肥发生了快速的生物固定。现有证据不支持eCO条件下其他的磷损失机制，包括由于牧草生长增加导致的无机磷消耗、通过植物→动物→粪便途径的磷吸收与归还增加，或磷向土壤剖面下层的移动。尽管如此，eCO和环境二氧化碳条件下的牧草磷浓度和吸收量相似，对磷敏感的豆科植物白三叶草的生物量在eCO条件下通常更大。因此，要么施肥制度足以维持牧草非限制性的磷状态，要么eCO条件下植物 - 土壤的综合生物调节弥补了有效磷的减少。如果补偿机制在eCO条件下支持作物磷营养方面发挥更大作用，但被侧重于无机磷的常规土壤有效磷测试所忽视，那么随着二氧化碳水平持续上升，将会出现磷肥过量施用的情况。
