Rice leaves and their functions

Rice leaves are composed of two main parts: leaf body and leaf sheath, as well as ear, ligule and other accessory organs. The place where the leaf sheath connects with the stem is called the leaf node. The place where the leaf sheath connects with the leaf body is called the leaf pillow. The first thing that grows when a seed germinates is the bud sheath, also known as sheath leaf, unearthed from the bud. The sheath leaf is different from other leaves. It is white and looks like a cylinder. The second leaf has only a leaf sheath and no leaf body, which is called an incomplete leaf. The leaf that begins from the third section has a leaf sheath and leaf body, which is called a complete leaf. The number of leaves of a variety should be calculated from the first complete leaf. The number of leaves from the first complete leaf to the differentiation of young spike is related to the maturity of the variety. The number of leaves of early-maturing varieties is less than that of late-maturing varieties. After the beginning of young panicle differentiation, the number of leaves grown by any variety is three. Therefore, the penultimate leaf begins to emerge, that is, the period when young panicle differentiation begins.

The leaves of rice before young panicle differentiation serve for rooting, tillering and leaves in the later stage of formation, and the nutrients needed for rice roots after young panicle differentiation are supplied by the penultimate leaves. According to research, 2/3 to 3/4 of the nutrients needed to enrich grains depend on the photosynthesis of the last few leaves. Therefore, strengthening the field management in the later stage, protecting the last few green leaves, especially the top sword leaf, from diseases and insect pests, in order to prolong their life, is an important measure to improve grain plumpness.

The importance of rice leaves lies in its photosynthesis. Rice leaves synthesize carbohydrates (glucose) using carbon dioxide absorbed by leaf stomata and water absorbed by roots and transported to leaves as raw materials and chlorophyll as media. This physiological activity is called photosynthesis, or assimilation. 90-95% of the dry matter of grain and straw produced by rice is organic matter produced by photosynthesis. The amount of photosynthesis in cloudy days is about 1/2 of that in sunny days. Photosynthesis on rainy or dark days is about 1/3 of that on sunny days. If the grain is filled with fruit in sunny weather, the grain is full. When the amount of light on both sides of rice leaves is equal, the photosynthesis on both sides is also equal. Therefore, the photosynthesis efficiency of straight leaves is high, while the efficiency of curved leaves is low. If there is not enough water in the leaves and the stomata on the leaves are closed, it will hinder the absorption of carbon dioxide by rice leaves, thus affecting photosynthesis. Therefore, the cultivation techniques should not be overweight in the middle stage, and do not cut off the water prematurely in the later stage, so as not to affect the yield.

The growth of rice leaves is closely related to air temperature, light, water and nutrients. When the air temperature is 32 ℃ and the soil temperature is 30-32 ℃, the leaves will stop growing when the temperature is below 7 ℃ or above 40 ℃. If the early rice seedlings encounter short-term low temperature (below 5-7 ℃), the young leaves that are forming and elongating in the leaf sheath will lose the ability to form chlorophyll. After protruding, the young leaf is all white, or part of it becomes white, and it is not easy to turn green after the weather turns warm.

Nitrogen fertilizer is the most important nutrient requirement for rice leaves. If the nitrogen fertilizer is sufficient, the leaf color is thick green, the growth is exuberant, and the photosynthesis is strong. When nitrogen is deficient, the leaves are yellowish, the leaves are narrow and small, and the photosynthates are less; on the contrary, if there is too much nitrogen fertilizer, the leaves are overextended, soft and sagging, resulting in shade, which will also affect photosynthesis and are prone to diseases. When phosphorus is deficient, the leaves are dark green, and the leaves are narrow and straight. When potassium deficiency, the leaf color is dark green, the leaf tip is yellow, the leaf is broad, thin, short and drooping. Therefore, the cultivation techniques should depend on the leaf color and leaf posture, and appropriate fertilizer and water management measures should be taken to obtain more photosynthates and achieve the goal of stable and high yield.