حساب العناصر المتفاعلة البيئي

حساب العناصر المتكافئة البيئي (أو يشار له على نطاق أوسع باسم "القياس الكيميائي البيولوجي) هو كيفية توازن الطاقة والعناصر على الأنظمة الحية. على غرار قياس اتحادية العناصر، حساب العناصر المتكافئة البيئي يقيس وفقاً لقيود محددة كتوازن الكتلة لأنها تنطبق على الكائنات الحية وتفاعلاتها في النظام البيئي. على وجه التحديد، كيف يؤثر توازن الطاقة والعناصر وكيف يتأثر هذا التوازن بالكائنات الحية وتفاعلاتها. ثمة تاريخ طويل لمفاهيم قياس اتحادية العناصر البيئي في علم البيئة، بالرجوع إلى الإشارات المبكرة لقيود توازن الكتلة التي وضعها ألفريد لوتكا ويوستوس فون ليبيغ وألفرد ريدفيلد. توسّعت هذه المفاهيم السابقة لربط عناصر علم وظائف الأعضاء للكائنات الحية بتفاعلات بشبكاتها الغذائية ووظيفة النظام البيئي.

Sheep feed on plant tissues that contain high concentrations of carbon relative to concentrations of nitrogen and phosphorus (i.e. a high ratio of C:N:P). To grow and develop, the tissues of a sheep need less carbon in relation to nitrogen and phosphorus (i.e. a low ratio of C:N:P) than the food eaten. The growth and development of any organism may be limited by unbalanced stoichiometry: an imbalance in the proportions of chemical elements in food that reflect proportions of physiologically important organic molecules.

Most work in ecological stoichiometry focuses on the interface between an organism and its resources. This interface, whether it is between plants and their تغذية النبات or large حيوانات عاشبة and نجيليةes, is often characterized by dramatic differences in the تركيب كيميائي of each part. The difference, or mismatch, between the elemental demands of organisms and the elemental composition of resources leads to an elemental imbalance. Consider أرضة, which have a tissue كربون:نيتروجين ratio (C:N) of about 5 yet consume خشب with a C:N نسبة (رياضيات) of 300–1000. Ecological stoichiometry primarily asks:

1. why do elemental imbalances arise in nature?
2. how is consumer علم وظائف الأعضاء and نظرية تاريخ الحياة affected by elemental imbalances? and
3. what are the subsequent effects on ecosystem processes?

Elemental imbalances arise for a number of physiological and تطورary reasons related to the differences in the biological make up of organisms, such as differences in types and amounts of جزيء ضخم, عضية خلوية, and نسيج حيوي. Organisms differ in the flexibility of their biological make up and therefore in the degree to which organisms can maintain a constant chemical composition in the face of variations in their resources. Variations in resources can be related to the types of needed resources, their relative availability in time and space, and how they are acquired. The ability to maintain internal chemical composition despite changes in the chemical composition and availability of resources is referred to as "stoichiometric استتباب". Like the general biological notion of استتباب, elemental homeostasis refers to the maintenance of elemental composition within some biologically ordered range. ضوئي التغذية organisms, such as طحالب and نباتات وعائية, can exhibit a very wide range of physiological plasticity in elemental composition and thus have relatively weak stoichiometric homeostasis. In contrast, other organisms, such as multicellular حيوان, have close to strict homeostasis and they can be thought of as having distinct chemical composition. For example, carbon to فسفور ratios in the suspended organic matter in بحيرةs (i.e., طحالب, bacteria, and حتات) can vary between 100 and 1000 whereas C:P ratios of برغوث الماء (جنس), a قشريات عوالق حيوانية, remain nearly constant at 80:1. The general differences in stoichiometric homeostasis between plants and animals can lead to large and variable elemental imbalances between consumers and resources.

Ecological stoichiometry seeks to discover how the chemical content of organisms shapes their ecology. Ecological stoichiometry has been applied to studies of دورة المغذيات, إقصاء تنافسي, animal growth, and nutrient limitation patterns in whole ecosystems. The Redfield ratio of the world's oceans is one very famous application of stoichiometric principles to ecology. Ecological stoichiometry also considers phenomena at the sub-cellular level, such as the P-content of a ريبوسوم, as well as phenomena at the whole biosphere level, such as the كيمياء الغلاف الجوي of غلاف الأرض الجوي.

To date the research framework of ecological stoichiometry stimulated research in various fields of biology, ecology, biochemistry and human health, including human microbiome research, cancer research, food web interactions, population dynamics, خدمات النظام البيئي, productivity of agricultural crops and honeybee nutrition.

طالع أيضاً

• تدفق الطاقة (علم البيئة)
• توازن الطاقة (أحياء)