湖南会同不同年龄杉木人工林土壤磷素特征

对湖南会同不同年龄(7年生、17年生、25年生)杉木人工林土壤全磷、有效磷、无机磷组分和有机磷进行了研究,结果表明:3种不同林龄杉木林土壤全磷和有效磷的含量分别在317.06—398.56 mg/kg和0.82—1.38 mg/kg之间,土壤全磷和速效磷含量均属低水平;杉木林土壤全磷含量从7年生幼龄林到25a近熟林出现先升高后降低的规律,并且17年生和25年生林分比7年生林分分别增加了19.68%、15.75%,土壤有效磷含量17年生和25年生林分比7年生林分提高了45.55%左右;土壤磷素活化系数均小于2.0%,这表明本研究区土壤全磷向速效磷转化较难,土壤中磷素的有效性较低,但该值随着林分年龄的增加而出现增大的现象;无机磷含量分别为:7年生169.50 mg/kg、17年生182.03 mg/kg、25年生175.94 mg/kg,从幼龄林到中龄林增高,中龄林以后降低;土壤中无机磷组分以O-P含量最高,其次是Fe-P,Ca-P,Al-P最少;杉木不同生长发育阶段对无机磷形态的吸收是有选择性的,幼龄林到中龄林阶段林木以吸收Al-P为主,近熟林阶段林木以吸收Fe-P和Ca-P为主;有机磷含量在全磷所占比例随林龄的变化来看,杉木生长过程中有部分的有机磷矿化为无机磷。土壤不同形态磷的相关性分析结果显示,土壤有效磷与有机磷相关系数为0.667,呈极显著相关性,是研究区杉木人工林土壤有效磷的主要来源。

Characteristics of soil phosphorus in different aged stands of Chinese fir plantations in Huitong, Hunan Province

Phosphorus (P) is an essential element for growth and development of plants. At cellular and sub-cellular levels, P plays a vital role in various important metabolic processes, such as protein synthesis, cell division, newborn tissues development and energy transformations. In terrestrial ecosystems, P is often the most limiting nutrient. This is particularly the case for some regions where nitrogen (N) in the soils is likely saturated due to high N deposition, extensive N fertilizer application and fossil fuel combustion. In this study, changes in P formations (total P, available P, inorganic P and organic P) in soils were investigated in three aged stands of Chinese fir plantations (7-, 17- and 25-year-old stands) in Huitong County, Hunan Province, China. The fractions of inorganic P in soils were also determined in the studied plantations. The purpose of this project is to examine the alterations of soil P in different aged Chinese fir forests. The results showed that the total P content ranged from 317.06 to 398.56 mg/kg and available P content from 0.82 to 1.38 mg/kg, in the three examined aged stands. The total P and available P contents were in a relative low level when compared with the corresponding values derived from the national soil survey. But the total P and available P contents in soils significantly increased with the aged stands. The average total P content in soils was about 19.68% and 15.75% higher in 17-year-old stands and 25-year-old stands than in 7-year-old stands. Available P content was about 45.55% higher in the 17- and 25-year-old stands than in the 7-year-old stands. P activation coefficient in the soils was low (< 2.0%) in the three aged stands of Chinese fir forests, which suggested that the transformation of organic P to available P was restricted, even certain mineralization indeed occurred in the studied site. The concentration of inorganic phosphorus was 169.50, 182.03 and 175.94 mg/kg in the 7-, 17- and 25-year-old stands, respectively. On average, the amount of inorganic P fractions in the studied soils was in an order: occluded bound P (O-P) > iron bound P (Fe-P) > calcium bound P (Ca-P) > aluminum bound P (Al-P). Significant changes in the patterns of absorption of inorganic phosphorus fraction occurred in different growth and developmental stages of Chinese fir forests. Typically, the Al-P fraction was the major component of the inorganic P absorbed by the tree in the 7- and 17-year-old plantations. But the Fe-P and Ca-P fractions became the most assimilated inorganic P in 25-year-old Chinese fir stands. It was found that there was a close relationship between the available P and organic P in soils with a correlation coefficient of 0.667 in the studied stands, which implied that the organic P was the main source of soil available P in Chinese fir plantations in the study region. The results suggested that it was likely an important management practice to increase the transform rate of inorganic P to available P in the younger stands in order to improve soil fertility and promote forest productivity. Our study provided a scientific basis and reference for better understanding of P storage and cycling in Chinese fir forests.