Decomposition and organic amendments chemistry explain contrasting effects on plant growth promotion and suppression of Rhizoctonia solani damping off

Organic Amendments (OAs) has been used in agroecosystems to promote plant growth and control diseases caused by soilborne pathogens. However, the role of OAs chemistry and decomposition time on plant growth promotion and disease suppression is still poorly explored. In this work, we studied the effect of 14 OAs at four decomposition ages (3, 30, 100, and 300 days) on the plant—pathogen system Lactuca sativa–Rhizoctonia solani. OAs chemistry was characterized via 13C-CPMAS NMR spectroscopy as well as for standard chemical (i.e. N content, pH, EC) and biological parameters (i.e. phytotoxicity and R. solani proliferation bioassay). OAs have shown variable effects, ranging from inhibition to stimulation of Lactuca sativa and Lepidium sativum growth. We recorded that N rich OAs with high decomposability were conducive in the short-term, while converting suppressive in the long term (300 days). On the other hand, cellulose-rich OAs with high C/N ratio impaired L. sativa growth but were more consistent in providing protection from damping-off, although this property has significantly shifted during decomposition time. These results, for the first time, highlight a consistent trade-off between plant growth promotion and disease control capability of OAs. Finally, we found that OAs effects on growth promotion and disease protection can be hardly predictable based on the chemical characteristic, although N content and some 13C CPMAS NMR regions (alkyl C, methoxyl C, and carbonyl C) showed some significant correlations. Therefore, further investigations are needed to identify the mechanism(s) behind the observed suppressive and conducive effects and to identify OAs types and application timing that optimize plant productivity and disease suppression in different agro-ecosystems.有机改良剂（Organic Amendments, OAs）已被广泛应用于农业生态系统，用以促进植物生长并防控土传病原菌引发的病害。然而，有机改良剂的化学特性与分解时长对植物生长促进及病害抑制的调控作用，目前仍未得到充分探究。 本研究针对14种有机改良剂，设置4个分解时长梯度（3天、30天、100天及300天），探究其对莴苣（Lactuca sativa）-立枯丝核菌（Rhizoctonia solani）这一植物-病原菌体系的影响。研究通过碳-13交叉极化/魔角旋转核磁共振波谱法（13C-CPMAS NMR spectroscopy），结合常规化学参数（如氮含量、pH值、电导率）与生物学参数（如植物毒性检测、立枯丝核菌增殖生物测定）对有机改良剂的化学特性进行表征。 实验结果显示，有机改良剂的作用效果存在显著差异，对莴苣与独行菜（Lepidium sativum）的生长可产生抑制或促进作用。研究发现，高可分解性且富氮的有机改良剂在短期分解后会促进病害发生，但在长期分解（300天）后则转变为具有病害抑制效果。与之相反，高碳氮比且富含纤维素的有机改良剂会抑制莴苣生长，但能更稳定地抵御猝倒病，不过该防护效果会随分解时长发生显著变化。 本研究首次明确了有机改良剂在植物生长促进与病害防控能力之间存在稳定的权衡关系。此外，尽管氮含量与部分碳-13交叉极化/魔角旋转核磁共振波谱特征区域（烷基碳、甲氧基碳与羰基碳）与上述效应存在显著相关性，但基于化学特性难以精准预测有机改良剂对植物生长促进与病害防护的实际效果。因此，未来仍需开展进一步研究，以阐明有机改良剂发挥病害抑制或促生作用的内在机制，并筛选出可在不同农业生态系统中优化植物生产力与病害抑制效果的有机改良剂类型及施用时机。