短期氮磷配施对刨花楠细根形态及其土壤微生物的影响

以1年生刨花楠幼苗为研究对象,通过不同的氮磷配施实验,采用扫描根系法和磷脂脂肪酸法,研究不同氮磷配施处理对刨花楠幼苗1—4级细根根序形态特征及其土壤微生物的影响。结果表明:(1)4种氮磷配施处理均显著增加了刨花楠1—2级根的比根长和比根面积(P0.05),降低了3—4级根的比根面积(P0.05);(2)通过不同梯度的氮磷配施,1—2级细根的根组织密度呈下降态势,而3—4级根的组织密度则显著增加(P0.05),体现低级根与高级根之间的权衡;(3)4种氮磷配施处理都显著降低刨花楠1—4级细根的平均直径(P0.05);(4)随着氮磷比的增加,微生物总量及细菌、真菌与放线菌数量等均呈现先增加后降低的趋势,并均在N∶P为10∶1时达到最大;(5)氮磷配施条件下,细菌、真菌等与1—2级细根的比根长和比根面积呈显著正相关,而与4级根的比根长和比根面积则呈显著负相关,革兰氏阳性菌、真菌等与3—4级根的组织密度存在显著正相关,而与1—2级根的组织密度无显著相关性。各级根序的平均直径均与土壤微生物无显著相关性。研究结果表明,短期氮磷配施以N∶P为10∶1的效果最好,其最有利于提高刨花楠苗木细根的养分吸收能力与养分吸收效率,苗木通过调整细根形态来适应氮沉降,其地下生物群落如土壤微生物及其与细根的关系也发生变化,进而影响地下生态系统碳氮循环和养分流动。

Effect of adding a combination of nitrogen and phosphorus on fine root morphology and soil microbes of Machilus pauhoi seedling

One-year old seedlings of Machilus pauhoi were used to determine the effect of adding a combination of N and P on the morphology of different orders of fine roots and soil microbes. For this, the phospholipid fatty acid (PLFA) analysis and root system scanning methods were used. The results were as follows:(1) Combined addition of N and P significantly improved (P < 0.05) specific root length and specific root area of the first-order and second-order fine roots, while it reduced specific root area of the third-order and fourth-order roots. (2) Root tissue density for the first-order and second-order fine roots tended to decline, contrary to that for the third-order and fourth-order. (3) Root average diameter of the first-order to the fourth-order roots was significantly reduced (P < 0.05). (4) Total microbial, fungal, and bacterial biomass all showed a tendency to reduce after first increasing, all reaching the maximum when treated with N:P in the ratio of 10:1. (5) Although the bacterial and fungal and actinomycetes biomass and total microbial were significantly and positively correlated with specific root length and specific root area for the first-and second-order roots, they were negatively correlated for the fourth-order roots. Although Gram-positive bacteria and fungal biomass were positive correlated with root tissue density for the third-order and the fourth-order, no significant correlations with the first-and second-order roots were observed. Root average diameter for all orders had no significant correlation with soil microbes. Our results suggest that the effect of short-term addition of a combination of N and P was the best when treated with N:P in the ratio of 10:1, which can improve the efficiency of nutrient uptake of Machilus pauhoi seedlings'' fine roots. Plants may adapt to N deposition by adjusting the fine root morphological characteristics. Meanwhile, the response of underground biological communities such as soil microbes, and the relationship of microbes with fine roots, to N deposition also changes, which affects C and N cycles and the nutrient flow in underground ecosystem.