Biochar amendments are widely promoted for increasing soil nutrient availability and plant yield, and although many plant species show positive growth responses, neutral to negative effects can also occur. Although biochar effects on plant yield may not yet be evident in the first growing season after amendment, foliar characteristics such as nitrogen (N) and chlorophyll concentrations are known to respond to changes in soil fertility and therefore may provide an early indication of plant performance. In this study, we investigated the effects of contrasting biochar treatments on soil nitrogen (N) forms and plant chlorophyll, and the relationships between soil and plant nitrogen status, for two economically important conifer species, Abies balsamea (L.) Mill and Picea pungens Englem., as well as forb and grass weeds. We applied two types of pyrolysis biochars (hereafter, USB and BGR) that differed in feedstock type (pine wood versus mixed forest harvesting residue) at contrasting application rates (low, high, and untreated control) to a fine sandy loam soil. We measured soil water content (SWC), pH, and inorganic nitrogen (NH₄⁺, NO₃⁻, and total inorganic N (TIN)), as well as plant foliar N, and chlorophyll content (Chl-a, -b, -ab), and fluorescence (Fv/Fm). SWC response was variable whereas all treatments except USB low increased pH. All treatments decreased inorganic N concentrations relative to the control, although differences diminished over the study period. USB high decreased Picea foliar N concentration whereas all treatments decreased grass foliar N. BGR decreased Abies Fv/Fm (low) and Picea Chl-a, Chl-ab (both levels), and Chl-b (low), whereas USB increased Abies Chl-ab (high). There was a weak positive relationship between foliar N and soil NH₄⁺ (r² = 0.14) and NO₃⁻ (r² = 0.11) in Abies seedlings, and between foliar N and TIN (r² = 0.16, 0.11) in both conifers. Abies foliar N showed a weak positive effect on Chl-a (r² = 0.22), Chl-b (r² = 0.10), and Chl-ab (r² = 0.22). Soil NO₃⁻ (r² = 0.14) and TIN (r² = 0.14) showed a weak negative correlation with Picea foliar Fv/Fm. This study shows that biochar type and amendment level influence soil and plant nitrogen responses, as well as their relationships, and responses may differ between plant species. Evaluating foliar characteristics shows promise as an early indicator of plant response to biochar, and may provide additional important information for evaluating contrasting biochars as potential sustainable soil amendments.

广泛推广了生物炭改良剂，以增加土壤养分的利用率和植物产量，尽管许多植物物种显示出积极的生长响应，但也可能发生中性至负面影响。尽管在改良后的第一个生长季中，生物炭对植物产量的影响可能尚不明显，但已知叶面特征（如氮（N）和叶绿素浓度）对土壤肥力的变化有反应，因此可能提供植物生长的早期迹象。在这项研究中，我们调查了两种比较经济的生物炭处理对土壤中氮（N）形态和植物叶绿素的影响，以及土壤和植物氮状况之间的关系，这是两种经济上重要的针叶树种：冷杉（Abies balsamea（L.）Mill和Picea pungens）Englem。，以及forb和草类杂草。我们将两种类型的热解生​​物炭（以下称为USB和BGR）以不同的施用量（低，高和未经处理的对照）以不同的原料类型（松木与混合森林采伐残余物）施用到了细砂壤土上。我们测量土壤水分含量（SWC），pH值，和无机氮（NH ₄ ⁺，NO ₃ ^- ，和总无机N（TIN）），以及植物叶面N，和叶绿素含量（叶绿素a，-b， -ab）和荧光（Fv / Fm）。SWC响应是可变的，而除USB以外的所有处理均会降低pH值。尽管研究期间差异有所减少，但所有处理均相对于对照降低了无机氮浓度。USB高降低云杉叶面氮浓度，而所有处理均降低了草叶面氮。BGR降低了Abies Fv / Fm（低）和Picea Chl-a，Chl-ab（两个水平）和Chl-b（低），而USB增加了Abies Chl-ab（高的）。有叶片N和土壤NH之间的弱的正相关关系₄ ⁺（R ²  = 0.14）和NO ₃ ^-（R ²  = 0.11）在冷杉苗，和叶面N和TIN（R之间² 在两种= 0.16，0.11）针叶树。冷杉叶面氮对Chl-a（r ²  = 0.22），Chl-b（r ²  = 0.10）和Chl-ab（r ² = 0.22）。土壤NO ₃ ^-（R ²  = 0.14）和锡（R ²  = 0.14）显示出与弱负相关云杉叶的Fv / FM。这项研究表明，生物炭的类型和修饰水平会影响土壤和植物的氮素反应，以及它们之间的关系，而且植物之间的反应可能会有所不同。评价叶面特性显示出有望作为植物对生物炭反应的早期指标，并可能为评估对比生物炭作为潜在的可持续土壤改良剂提供其他重要信息。