Photosynthesis

The rate of photosynthesis can be limited by light levels and carbon uptake. However, resource availability and competition are also limiting to tree growth. Trees need water and minerals in order to grow. Specifically, trees need large amounts of nitrogen and phosphorus. However, these nutrients are often limiting because they are needed in greater quantities than available in soil. Nitrogen is needed for growth, reproduction, and photosynthesis. It exists in organic and inorganic forms in soil, however trees can only uptake two major inorganic forms, nitrate and ammonium. Therefore, trees have to rely on nitrogen-fixing organisms in order to obtain the amounts of nitrogen necessary for survival. Likewise, phosphorus is present in soil in organic and inorganic forms, but it is not always available for the tree to uptake. Phosphorus binds tightlyto particles in the soil that make it hard for the trees to access. Trees also have to rely on other organisms in order to receive most of their phosphorus. They can get it from microbial activity or decomposition of microbes or other organisms. Additionally, the soil composition effects the amount of nutrients and water a tree can access.  Large soil particles hold a greater amount of water than coarse soils. Since nitrogen is taken up by roots mainly through bulk transportation of water through the xylem, soil particle size can limit the amount of water and minerals taken up by trees. Another way soil can play a role in nutrient availability is through cation exchange capacity. A soil that has a large cation exchange capacity is able to attract and hold ammonium, reducing the amount of nitrogen leached from the soil.