不同林龄杉木人工林根际土添加对其幼苗菌根侵染及生长的影响

【目的】研究不同林龄杉木人工林根际土添加对杉木无菌幼苗生长的影响,为杉木合理的菌根化育苗提供理论基础。【方法】选取苗龄4个月的杉木无菌幼苗为材料,移栽至无菌基质土中,在幼苗根系附近分别添加(150±2)g的杉木幼龄林根际土(RS1)、中龄林根际土(RS2)、近熟林根际土(RS3)、成熟林根际土(RS4)、过熟林根际土(RS5),同时设置对照(CK)处理。添加前测定根际土养分含量、酸碱度、丛枝菌根真菌(AMF)孢子密度,并于移栽后1年测定杉木幼苗根系AMF侵染率、基质土养分含量、酸碱度,测量杉木幼苗形态指标、计算生物量。【结果】表明:不同林龄杉木人工林根际土的养分含量、酸碱度、AMF孢子密度有差异,其添加对杉木幼苗根系侵染率提高有显著促进作用,幼苗根系AMF侵染率与所添加林分根际土中AMF孢子密度有极显著正相关关系,侵染率呈现RS5>RS4>RS3>RS1>RS2>CK的规律。杉木林分根际土的添加对杉木幼苗地径、苗高、根长、冠幅、基生枝条数、生物量累积等也有促进作用,添加过熟林根际土(RS5)的处理在促进杉木幼苗生长方面优于其他4种根际土。【结论】杉木林分根际土可以作为菌剂添加进行杉木幼苗的菌根化育苗,增加根系菌根侵染率,促进幼苗的高质量生长,这对杉木育苗及菌根真菌在林业上的应用具有重要实践意义。

The variation of nutrient concentration in the rhizosphere of larch and ash in mixed and monoculture stands

Soil samples were taken from rhizosphere zone and off-rhizosphere zone of ash (Fraxinus mandshurica Rupr.) and larch (Larix olgensis Henry) in mixed and monoculture stands, and the nutrient concentration of N, P, and K was analyzed to study the effect of nutrients variation on yield improvement in the mixed stand. The result showed that: 1) The stand level total soil N concentration and available N in the mixed stand was similar to that in the monoculture stand of ash, but higher than that in monoculture stand of larch. The total N and available N concentration in rhizosphere soil of ash in the mixed stand was similar to that in the monoculture stand of ash, but the available N concentration in rhizosphere of larch in mixed stand was much higher than in its monoculture. 2) The stand level total P, total K concentration in the mixed stand was similar to that in monocul-ture stands of both species, but available P and K was more concentrated in the mixed stand than in the monoculture stands of ash. The rhizosphere available P and K of ash in the mixed stand was 44.1% and 13.5% (for the 9-yr-old stands) and 79.6% and 25.6% (for the 21-yr-old stands) higher than that in its monoculture. The improvement of soil P and K availability in the mixed stand is concluded.

Isolation and Identification of Phosphobacteria in PoplarRhizosphere from Different Regions of China

A few soil microorganisms can convert insoluble forms of phosphorus （P） to an accessible form to increase plant yields The objectives of this study were to isolate, screen and identify the phosphobacteria, i.e., phosphate-solubilizing bacteria （PSB） and phosphate-mineralizing bacteria （PMB）, in some poplar plantations and to select potential microbial inoculants that could increase the P uptake by plants. Seventy four PSB strains and 138 PMB strains were preliminarily screened from 797＂colonies isolated from the rhizosphere soil of poplar by the visible decolorization in the National Botanical Research Institute＇s phosphate growth medium （NBRIP） containing a pH indicator of bromophenol and by the clear/halo zone on yeast malt agar plate, respectively. Then, based on the solubilization of Ca3（PO4）2 in liquid NBRIP medium and the mineralization of lecithin in liquid Menkina medium, 15 PS1R strains and 7 PMB strains were further determined for their abilities to solubilize Ca3（PO4）2 and to mineralize lecithin. The results showed that the 15 PSB strains exhibited inorganic P-solubilizing abilities ranging between 376.62 and 669.56 mg L-1 and the 7 PMB strains exhibited organic P-mineralizing abilities vaxying from 0.32 to 1.56 mg L-1 three days after incubation. Three of PSB strains with the highest P-solubilizing ability, named JW-JS1, JW-JS2 and JW-SX2, were all preliminarily identified as Pseudomonas ftuorescens, while two of PMB strains with the highest P-mineralizing ability, named JYZ-SD1 and JYT-JS2, were preliminarily identified as Bacillus cereus and Bacillus subtilis, respectively. All the efficient PSB and PMB strains should be further studied under both pot culture and field conditions to test their beneficial effects on poplar.