State University of New York College of Environmental Science and Forestry, Syracuse, NY, United States of America.
California Department of Fish and Wildlife, Sacramento, CA, United States of America.
PeerJ. 2022 Apr 21;10:e13193. doi: 10.7717/peerj.13193. eCollection 2022.
Foliar chemistry can be useful for diagnosing soil nutrient availability and plant nutrient limitation. In northern hardwood forests, foliar responses to nitrogen (N) addition have been more often studied than phosphorus (P) addition, and the interactive effects of N and P addition have rarely been described. In the White Mountains of central New Hampshire, plots in ten forest stands of three age classes across three sites were treated annually beginning in 2011 with 30 kg N ha y or 10 kg P ha y or both or neither-a full factorial design. Green leaves of American beech ( Ehrh.), pin cherry ( L.f.), red maple ( L.), sugar maple ( Marsh.), white birch ( Marsh.), and yellow birch ( Britton) were sampled pre-treatment and 4-6 years post-treatment in two young stands (last cut between 1988-1990), four mid-aged stands (last cut between 1971-1985) and four mature stands (last cut between 1883-1910). In a factorial analysis of species, stand age class, and nutrient addition, foliar N was 12% higher with N addition ( < 0.001) and foliar P was 45% higher with P addition ( < 0.001). Notably, P addition reduced foliar N concentration by 3% ( = 0.05), and N addition reduced foliar P concentration by 7% ( = 0.002). When both nutrients were added together, foliar P was lower than predicted by the main effects of N and P additions ( = 0.08 for N × P interaction), presumably because addition of N allowed greater use of P for growth. Foliar nutrients did not differ consistently with stand age class ( ≥ 0.11), but tree species differed ( ≤ 0.01), with the pioneer species pin cherry having the highest foliar nutrient concentrations and the greatest responses to nutrient addition. Foliar calcium (Ca) and magnesium (Mg) concentrations, on average, were 10% ( < 0.001) and 5% lower ( = 0.01), respectively, with N addition, but were not affected by P addition ( = 0.35 for Ca and = 0.93 for Mg). Additions of N and P did not affect foliar potassium (K) concentrations ( = 0.58 for N addition and = 0.88 for P addition). Pre-treatment foliar N:P ratios were high enough to suggest P limitation, but trees receiving N ( = 0.01), not P ( = 0.64), had higher radial growth rates from 2011 to 2015. The growth response of trees to N or P addition was not explained by pre-treatment foliar N, P, N:P, Ca, Mg, or K.
叶片化学分析有助于诊断土壤养分供应状况和植物养分限制情况。在北方硬木林中，氮（N）添加的叶片响应比磷（P）添加的叶片响应更常被研究，而 N 和 P 添加的交互作用则很少被描述。在新罕布什尔州中部的白山地区，三个地点的十个林分中的样地从 2011 年开始每年接受 30 公斤 N ha y 或 10 公斤 P ha y 或两者都接受或两者都不接受-这是一个完全析因设计。在两个年轻的林分（最后一次砍伐在 1988-1990 年之间）、四个中龄林分（最后一次砍伐在 1971-1985 年之间）和四个成熟林分（最后一次砍伐在 1883-1910 年之间）中，在处理前和处理后 4-6 年采集了美洲山毛榉（ Ehrh.）、黑樱桃（ L.f.）、红枫（ L.）、糖枫（ Marsh.）、白桦（ Marsh.）和黄桦（ Britton）的绿叶样本。在物种、林龄类和养分添加的析因分析中，叶片 N 增加了 12%（<0.001），叶片 P 增加了 45%（<0.001）。值得注意的是，P 添加减少了 3%的叶片 N 浓度（=0.05），N 添加减少了 7%的叶片 P 浓度（=0.002）。当同时添加两种养分时，叶片 P 低于 N 和 P 添加的主效应预测值（=0.08，用于 N × P 交互作用），大概是因为添加 N 允许 P 更多地用于生长。叶片养分与林龄类没有一致的差异（≥0.11），但树种不同（≤0.01），先锋树种黑樱桃的叶片养分浓度最高，对养分添加的反应最大。叶片钙（Ca）和镁（Mg）浓度分别平均降低了 10%（<0.001）和 5%（=0.01），这是由于 N 添加的结果，但不受 P 添加的影响（Ca 的=0.35，Mg 的=0.93）。N 和 P 的添加均未影响叶片钾（K）浓度（N 添加的=0.58，P 添加的=0.88）。处理前叶片 N:P 比高到足以表明 P 限制，但接受 N（=0.01）而不是 P（=0.64）的树木，从 2011 年到 2015 年的径向生长速度更高。树木对 N 或 P 添加的生长反应不能用处理前叶片 N、P、N:P、Ca、Mg 或 K 来解释。
