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Forest canopies are the functional interface between ecosystem and the atmospheric nitrogen (N) deposition. However, the sources of spatio‐temporal variability and intra‐event variation of N deposition via throughfall (TF) remain ambiguous. Here, we analysed TF samples for concentrations and fluxes of ammonium (NH4+) and nitrate (NO3−) using an array of 20 fixed‐position collectors on an event and within event basis throughout the 2019 growing season in a Chinese pine plantation, Northern China. Results showed that the volume weighted mean concentrations of NH4+ and NO3− in TF were significantly higher than those in bulk precipitation (BP) during the study period. A canopy budget model indicated that canopy uptake was more dominant than dry deposition for NH4+, while the reverse was true for NO3−. This caused a comparable TF NH4+ flux but an enhanced TF NO3− fluxes compared to BP. The intra‐event trend and magnitude of TF NH4+ and NO3− concentrations were influenced by the antecedent dry period and rainfall intensity, and indicated that biological nitrification may occur in the canopies. In addition, due to the larger of canopy NH4+ uptake that counteracted the amplifying effect of dry deposition, the spatial variability of TF NH4+ concentration was significantly lower than that of TF NO3− concentration, and exhibited more temporal persistence. No relationship was found between the spatial distribution of TF NH4+ concentration and the TF amount, the distance to the nearest trunk, nor the canopy cover, whereas the TF NO3− concentration was significantly related to the TF amount and the canopy cover. These findings can enhance our understanding of N processes within canopies, and have important implications for evaluating the impacts of N deposition in forest ecosystems. [ABSTRACT FROM AUTHOR]

Canopy closure (CC) is an important parameter in many fields. It can be obtained from digital hemispherical photographs (DHPs) by converting the pixels to black or white according to their nature: canopy or not. DHP exposure is a key factor that controls accuracy in CC determination. Many accurate pre- and post-treatments exist for enhancing the exposure, but these methods often require specific knowledge. To be more “user-friendly” compared to the raw equations provided in the literature, we have proposed a new software, DHPT 1.0, that calculates CC from DHPs using hue-enhancing methods before an automatic thresholding calculation. DHPT 1.0 does not require manual settings, thus avoiding errors caused by operator misjudgement. The first step of this study was to calibrate the enhancement methods to make DHPT 1.0 able to accurately calculate CC regardless of the photograph exposure. We have therefore used 210 digital photographs that regroup seven locations along a visual gradient of CC and of exposures. After calibration, the accuracy of DHPT 1.0 was compared with the accuracy of three software packages that are widely used by experts: Canopon2, GLA 2.0, and WINPHOT 5.0. A batch of two sets of 10 DHPs divided into one set of over-exposed DHPs and one set of under-exposed DHPs from 10 locations along a gradient of CC was used for the comparison. DHPT 1.0 provides the most accurate results, with an average error of 8% between the same under-saturated or over-saturated DHP. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigated the contribution of three evapotranspiration (ET) components including canopy interception ( Ei), tree transpiration ( Et) and forest floor evaporation ( Ef) and identified the sources depth of evaporated water in a Japanese cypress stand. Monitoring primarily focused on the growing season of July-October 2011. In a 12 × 13 m plot with 28 trees with a DBH of 19.1 ± 3.9 cm, Ei was calculated as the difference between precipitation on an open field and precipitation under a canopy as the sum of throughfall and stemflow, and Et was measured using the Granier method. Ef was measured by weighing lysimeters. Total ET during the monitoring period was 446.3 mm, accounting for 47.5% of the total precipitation of 938.8 mm. Ei was the dominant evaporation flux and accounted for 53.6% of ET or 25.5% of rainfall, followed by Et with 33.7% of ET or 16.0% of rainfall. The average Et was 1.5 ± 0.6 mm d−1. It was well correlated with soil moisture at a depth of 5-15 cm, which reflected the forest properties, i.e. tree roots were exposed on the forest floor. Ef accounted for 12.7% of ET or 6.0% of rainfall with a daily mean of 0.55 ± 0.26 mm d−1, and was best correlated with soil moisture in the upper 5 cm of soil. These results can improve the understanding of water budget in forested watershed and also be used to build and validate hydrologic models for water resource managements. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• TF , SF and Ei had no significant differences between UP and LP. • TF NO 3 −-N and SO 4 2−-S fluxes were slightly/significantly lower in UP compared to LP. • SF NO 3 −-N and SO 4 2−-S fluxes were quite similar between the two slope plots. • NTF NO 3 −-N and SO 4 2−-S fluxes were negative at both UP and LP. • Canopy exchange may be dominant factor on these hydrochemical fluxes in watershed. Forest canopies create a high spatial variability of both canopy interception (Ei) and acid deposition. However, spatial characteristics of these hydrochemical fluxes along a slope gradient in forest watersheds remain unclear. Here we monitored bulk precipitation (BP), throughfall (TF), stemflow (SF), and associated nitrate (NO 3 −) and sulfate (SO 4 2−) in an upper slope plot (UP) and a lower slope plot (LP) in a subtropical broadleaved forest, Southeast China. Results showed that annual rates of TF , SF and Ei to BP in UP were 85.2%, 2.6%, and 12.2%, respectively. Corresponding values in LP were 88.6%, 2.2%, and 9.2%. There were no significant differences among these rainfall partitioning components between UP and LP. Additionally, annual volume weighted mean concentrations of NO 3 −-N in TF and SF were significantly lower than in BP , whereas no significant differences were found for SO 4 2−-S among BP , TF and SF. Unlike annual TF NO 3 −-N fluxes were similar in UP and LP, annual TF SO 4 2−-S fluxes significantly increased along the UP to LP. Net TF + SF (NTF) fluxes were negative for NO 3 −-N and SO 4 2−-S at the two slope plots, illustrating retained/uptake in the canopy. Dormant season NTF S fluxes were close to zero, indicating that dry deposition does not appear to play a major role, whereas exchange with foliage surfaces should be the dominant factor controlling the spatial patterns of TF N and S fluxes in the watershed. This study can contribute to the evaluation of watershed-scale water and acidifying input into the soil during canopy passage, and further consequent effects on forest ecosystems. [ABSTRACT FROM AUTHOR]