ABSTRACT
With the rapid development of dense apple tree plantings with the dwarf rootstock cultivation method, determining accumulation and distribution characteristics of soil mineral nitrogen in densely planted orchards with dwarf rootstock is important to enable scientific fertilization of apple orchards. We investigated densely planted apple orchards with dwarf rootstocks and different plant ages (6 a, 9 a, and 12 a). We collected soil samples under trees, between trees, between rows, and at the midpoints between the trees and rows, and examined the accumulation and distribution characteristics of nitrate, ammonium, and mineral nitrogen. The cumulative amount of nitrate in the 0-300 cm soil layer increased with plant age. The difference between orchards with different plant ages was significant and showed the trend 6 a<9 a<12 a. The cumulative amount of nitrate increased from 1729 kg·hm-2 to 3771 kg·hm-2 with increasing plant age. The ammonium content was low for orchards of all plant ages and had little effect on the accumulation and spatial distribution of mineral nitrogen. There were two accumulation peaks of nitrate nitrogen in the vertical direction. The depth of soil layer where the second accumulation peak was located decreased from 180 cm to 220 cm with increasing plant age. In the horizontal direction, soil nitrate nitrogen content between rows increased from 27 mg·kg-1 to 138 mg·kg-1 with increasing plant age, representing a more than 400% increase. The difference between orchards with different plant ages was significant. In summary, excessive usage of nitrogen fertilizer and serious leaching of nitrate were problematic in all orchards with different ages. Less nitrogen fertilizer should be applied, and anti-seepage measures should be used at the fertilization location to prevent the leaching of nitrate to deep layers.
Subject(s)
Malus , Soil , China , Fertilizers , Minerals , Nitrates/analysis , Nitrogen/analysis , Water/analysisABSTRACT
Drought is one of the most severe threats to the growth, development and yield of plant. In order to unravel the molecular basis underlying the high tolerance of pitaya (Hylocereus undatus) to drought stress, suppression subtractive hybridization (SSH) and cDNA microarray approaches were firstly combined to identify the potential important or novel genes involved in the plant responses to drought stress. The forward (drought over drought-free) and reverse (drought-free over drought) suppression subtractive cDNA libraries were constructed using in vitro shoots of cultivar 'Zihonglong' exposed to drought stress and drought-free (control). A total of 2112 clones, among which half were from either forward or reverse SSH library, were randomly picked up to construct a pitaya cDNA microarray. Microarray analysis was carried out to verify the expression fluctuations of this set of clones upon drought treatment compared with the controls. A total of 309 expressed sequence tags (ESTs), 153 from forward library and 156 from reverse library, were obtained, and 138 unique ESTs were identified after sequencing by clustering and blast analyses, which included genes that had been previously reported as responsive to water stress as well as some functionally unknown genes. Thirty six genes were mapped to 47 KEGG pathways, including carbohydrate metabolism, lipid metabolism, energy metabolism, nucleotide metabolism, and amino acid metabolism of pitaya. Expression analysis of the selected ESTs by reverse transcriptase polymerase chain reaction (RT-PCR) corroborated the results of differential screening. Moreover, time-course expression patterns of these selected ESTs further confirmed that they were closely responsive to drought treatment. Among the differentially expressed genes (DEGs), many are related to stress tolerances including drought tolerance. Thereby, the mechanism of drought tolerance of this pitaya genotype is a very complex physiological and biochemical process, in which multiple metabolism pathways and many genes were implicated. The data gained herein provide an insight into the mechanism underlying the drought stress tolerance of pitaya, as well as may facilitate the screening of candidate genes for drought tolerance.
