08-13-2021-0111- Photorespiration

Photorespiration (also known as the oxidative photosynthetic carbon cycle, or C₂ photosynthesis) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle. This process reduces the efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in C₃ plants.^[1]Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria.

The oxygenation reaction of RuBisCO is a wasteful process because 3-phosphoglycerate is created at a reduced rate and higher metabolic cost compared with RuBP carboxylase activity. While photorespiratory carbon cycling results in the formation of G3P eventually, around 25% of carbon fixed by photorespiration is re-released as CO
2^[2] and nitrogen, as ammonia. Ammonia must then be detoxified at a substantial cost to the cell. Photorespiration also incurs a direct cost of one ATP and one NAD(P)H.

While it is common to refer to the entire process as photorespiration, technically the term refers only to the metabolic network which acts to rescue the products of the oxygenation reaction (phosphoglycolate).

https://en.wikipedia.org/wiki/Photorespiration

Photorespiration

Photorespiration refers to a process in plant metabolism where the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) oxygenates Ribulose-1,5-bisphosphate (RuBP), wasting some of the energy produced by photosynthesis.

From: Reference Module in Life Sciences, 2020

https://www.sciencedirect.com/topics/medicine-and-dentistry/photorespiration

 All plants require sufficient supplies of macronutrients for healthy growth, and nitrogen (N) is a nutrient that is commonly in limited supply. Nitrogen deficiency in plants can occur when organic matter with high carbon content, such as sawdust, is added to soil.^[1] Soil organisms use any nitrogen to break down carbon sources, making N unavailable to plants.^[1] This is known as "robbing" the soil of nitrogen. All vegetables apart from nitrogen fixing legumes are prone to this disorder.

Nitrogen deficiency can be prevented in the short term by using grass mowings as a mulch, or foliar feeding with manure, and in the longer term by building up levels of organic matter in the soil. Sowing green manure crops such as grazing rye to cover soil over the winter will help to prevent nitrogen leaching, while leguminous green manures such as winter tares will fix additional nitrogen from the atmosphere.

https://en.wikipedia.org/wiki/Nitrogen_deficiency