| Abstrakt: |
• We measured whole-tree standing N pools for different genotypes across a rotation. • Differences in N pools among genotypes mostly reflected differences in tissue mass. • Ephemeral N pools fluctuated, while perennial N pools increased through time. • Genotype and resource availability influenced the distribution of N pools. • Belowground N pools accounted for > 24 % of standing N for all genotypes. Our understanding of the accretion and distribution of tree tissue nitrogen (N) pools across a variety of species and genotypes suitable for short-rotation woody crop (SRWC) production in response to water and N availability remains limited. We measured dormant-season, rotation-length, whole-tree N pools for five tree genotypes from four species (two eastern cottonwood, Populus deltoides Bartr., genotypes; American sycamore, Platanus occidentalis L.; American sweetgum, Liquidambar styraciflua L.; and loblolly pine, Pinus taeda L.) receiving irrigation (I), fertilization (F), their combination (IF), or no resources manipulation (C). Our results demonstrate that foliar nitrogen concentration [N] responded to fertilization but was constrained within genotype-specific ranges and varied temporally. Tree genotypes differed in their composite and component tissue N content (N C), and these differences mostly reflected tissue mass (i.e., larger components and trees resulted in higher N C). Resource amendments (I , F , IF) resulted in up to 3.8-fold increases in N C compared with C , which were most pronounced for sycamore and sweetgum with F and IF treatments, respectively. By the end of the rotation, forest stands accumulated 73 to 452 kg N ha−1 in tree tissues with 40 – 78 % distributed aboveground and 22 – 60 % distributed belowground. A critical difference between genotypes was that all hardwoods exhibited larger belowground N distributions than the evergreen conifer. Our results stress the importance of belowground N pools and highlight differences among genotypes. Our study underscores valuable information about N pools across genotypes suitable for SRWC production, which can be leveraged to inform fertilization plans and devise sustainable nutrient management as production expands across marginal lands. [ABSTRACT FROM AUTHOR] |
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